Tuesday, July 29, 2008

* Notes On The Troubleshooting And Repair Of Television Sets

************************************************************************ * Notes On The Troubleshooting And Repair Of Television Sets * * * * **** Version 2.65 **** * * * * Copyright (C) 1994,1995,1996,1997,1998 * * Samuel M. Goldwasser * * Corrections or suggestions to: sam@stdavids.picker.com * * * * --- All Rights Reserved --- * * * * Reproduction of this document in whole or in part is permitted * * if both of the following conditions are satisfied: * * * * 1. This notice is included in its entirety at the beginning. * * 2. There is no charge except to cover the costs of copying. * * * ************************************************************************ **************** Introduction **************** Television at the crossroads:---------------------------- Television in substantially its present form has been with us for nearly50 years. It is a tribute to the National Television Standards Committee(NTSC) that the color television standards agreed upon in the early 1950shave performed remarkably well making quite efficient use of valuable radiospectrum space and the psychovisual characteristics of the human eye-brainsystem. However, HDTV (High Definition TV) will supplant and ultimatelyreplace the current standards. We will all come to expect its superiorresolution, freedom from noise and ghosting, and pure CD sound. Yet, theperceived quality of TV broadcasts and cable will never likely be the majorissue with most consumers. Content will continue to be the biggest problem. It is likely that in roughly 15 years, HDTV - digitally processed andtransmitted as 1s and 0s - will completely replace the current system.Acceptance in the marketplace is by no means assured but with the mergingof TV and computers - with the Internet as a driving force - it would seemthat the days of the stand-alone analog TV set are numbered. Television receiver fundamentals:-------------------------------- The basic color television receiver must perform the same functions today as40 years ago. (Since B/W is a subset of the color standard, most referencesin this document will be for color except as noted). A studio video monitor includes all of the functions of a television receiver except the tunerand IF (which rarely fail except for bad connections or perhaps lightningstrikes to the antenna or cable connection). Therefore mostof the repair information in this document is applicable to both TVs andstudio monitors. Modern computer monitors share many similarities withTVs but the multisync and high scan rate deflection circuitry and moresophisticated power supplies complicates their servicing. As of this writing, all but the smallest TVs are based on the CathodeRay Tube (CRT) as the display device. Tiny pocket sets, camcorderviewfinders, and the like have started using LCD (Liquid Crystal Display)panels but these are still inferior to the CRT for real time video.There has always been talk of 'the picture on the wall' display. Whilewe are closer than ever to this possibility, I believe that mass productionof an affordable wall mural TV screen is still decades away. The reasonis simple economics - it is really hard to beat the simplicity of theshadow mask CRT. For example, a decent quality active matrix color LCDpanel may add $1000 to the cost of a notebook computer compared to $200for a VGA monitor. More of these panels go in the dumpster than make itto product do to manufacturing imperfections. Projection - large screen - TVs may, on the other hand, be able to takeadvantage of a novel development in integrated micromachining - theTexas Instruments Inc. Digital Micromirror Device (DMD). This is basicallyan integrated circuit with a tiltable micromirror for each pixel fabricatedon top of a static memory - RAM - cell. This technology wouldpermit nearly any size projection display to be produced and wouldtherefore be applicable to HDTV. Since it is a reflective device, thelight source can be as bright as needed. However, this is still nota commercial product but stay tuned. TV repair:--------- Unlike VCRs or CD players where any disasters are likely to only affectyour pocketbook, TVs can be dangerous. Read, understand, and follow theset of safety guidelines provided later in this section whenever workingon TVs, monitors, or other similar high voltage equipment. If you do go inside, beware: line voltage (on large caps) and high voltage(on CRT) for long after the plug is pulled. There is the added danger ofCRT implosion for carelessly dropped tools and often sharp sheetmetalshields which can injure if you should have a reflex reaction upon touchingsomething you should not touch. In inside of a TV or monitor is no placefor the careless or naive. Having said that, a basic knowledge of how a TV set works and what cango wrong can be of great value even if you do not attempt the repair yourself. It will enable you to intelligently deal with the service technician. Youwill be more likely to be able to recognize if you are being taken for a rideby a dishonest or just plain incompetent repair center. For example, afaulty picture tube CANNOT be the cause of a color television only displayingshows in black-and-white. The majority of consumers probably do not know eventhis simple fact. Such a problem is usually due to a bad capacitor or other10 cent part. This document will provide you with the knowledge to deal with a largepercentage of the problems you are likely to encounter with your TVs.It will enable you to diagnose problems and in many cases, correct themas well. With minor exceptions, specific manufacturers and modelswill not be covered as there are so many variations that such a treatment wouldrequire a huge and very detailed text. Rather, the most common problemswill be addressed and enough basic principles of operation will be providedto enable you to narrow the problem down and likely determine a course ofaction for repair. In many cases, you will be able to do what is requiredfor a fraction of the cost that would be charged by a repair center. Should you still not be able to find a solution, you will have learned a greatdeal and be able to ask appropriate questions and supply relevant informationif you decide to post to sci.electronics.repair. It will also be easier to dofurther research using a repair text such as the ones listed at the end ofthis document. In any case, you will have the satisfaction of knowing youdid as much as you could before taking it in for professional repair.With your new-found knowledge, you will have the upper hand and will noteasily be snowed by a dishonest or incompetent technician. Repair or replace:----------------- If you need to send or take the TV to a service center, the repaircould easily exceed half the cost of a new TV. Service centersmay charge up to $50 or more for providing an initial estimate of repaircosts but this will usually be credited toward the total cost of the repair(of course, they may just jack this up to compensate for their bench time). TV prices have been dropping almost as fast as PC prices. Therefore, payingsuch prices for repair just may not make sense. Except for picture tubeproblems, most TV faults can be corrected without expensive parts, however.Keeping a 5 year old TV alive may be well worthwhile as basic TV performanceand important features have not changed in a long time. If you can do the repairs yourself, the equation changes dramatically asyour parts costs will be 1/2 to 1/4 of what a professional will chargeand of course your time is free. The educational aspects may also beappealing. You will learn a lot in the process. Thus, it may make senseto repair that old clunker for your game room or beach house. (I wouldsuggest the kid's room but most TV watching just rots the brain anyhow soa broken TV may be more worthwhile educationally than one that works.) ******************* TV Receivers 101 ******************* Subsystems of a television set:------------------------------ A TV set includes the following functional blocks: 1. Low voltage power supply (some may also be part of (2)). Most of the lower voltages used in the TV may be derived from the horizontal deflection circuits. Sometimes, there is a separate switching power supply but this would be the exception. Rectifier/filter capacitor/regulator from AC line provides the B+ to the switching power supply or horizontal deflection system. Degauss operates off of the line whenever power is turned on (after having been off for a few minutes) to demagnetize the CRT. 2. Horizontal deflection. These circuits provide the waveforms needed to sweep the electron beam in the CRT across and back some 15,734 times per second (for NTSC). The horizontal sync pulse from the sync separator locks the horizontal deflection to the video signal. 3. Vertical deflection. These circuits provide the waveforms needed to sweep the electron beam in the CRT from top to bottom and back 60 times per second (for NTSC). The vertical sync pulse from the sync separator locks the vertical deflection to the video signal. 4. CRT high voltage (also part of (2)). A modern color CRT requires up to 30 KV for a crisp bright picture. Rather than having a totally separate power supply, nearly every TV on the planet derives the HV (as well as many other voltages) from the horizontal deflection using a special transformer called a 'flyback' or 'Line OutPut Transformer (LOPT) for those of you on the other side of the lake. 5. Tuner, IF, AGC, video and audio demodulators. Input is the antenna or cable signal and output are baseband video and audio signals. There is usually someplace inside the TV where line level video and audio are present but it may not be accessible from the outside of the cabinet unless you paid for the more expensive model with the A/V option. Very often, the tuner is a shielded metal box positioned on the bottom right (as viewed from the front) separate from the main circuit board. Sometimes it is on the main circuit board. The IF section may be in either place. On older or cheap TVs with a knob tuner, this is usually mounted to the front panel by itself. There are usually separate boxes for the VHF and UHF tuners. 6. Chroma demodulator. Input is the baseband video signal. Outputs are the individual signals for the red, green, and blue video to the CRT. 7. Video drivers (RGB). These are almost always located on a little circuit board plugged directly onto the neck of the CRT. They boost the output of the chroma demodulator to the hundred volts or so needed to drive the cathodes of the CRT. 8. Sync separator. Input is baseband video. Output is horizontal and vertical sync pulses to control the deflection circuits. 9. Audio amplifier/output. The line level audio is amplified to drive a set of speakers. If this is a stereo TV, then these circuits must also perform the stereo demultiplexing. 10. System control. Most modern TVs actually use a microcontroller - a fixed program microcomputer to perform all user interface and control functions from the front panel and remote control. These are becoming increasingly sophisticated. However, they do not fail often. Older TVs use a bunch of knobs and switches and these are prone to wear and dirt. Most problems occur in the horizontal deflection and power supply sections.These run at relatively high power levels and some components run hot.The high voltage section is prone to breakdown and arcing as a resultof hairline cracks, humidity, dirt, etc. The tuner components are usually quite reliable unless the antenna experiencesa lightning strike. However, it seems that even after 20+ years ofsolid state TVs, manufacturers still cannot reliably solder the tunerconnectors and shields so that bad solder connections in these areas arecommon even in new sets. Why projection TVs are not just normal TVs in big boxes:------------------------------------------------------- In order to achieve the necessary brightness with a large display format,three separate monochrome CRTs are used with optics to combine the three imagesproperly at the screen. This creates an entire set of additional problems indesign. (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). The average projection TV has about twice as many parts as its direct-viewcounterpart. Some of the extra parts are essential for projection because CRTprojection tubes require dynamic convergence. The other extra parts have to dowith the fact that a more expensive TV also should have some extra features,like Dolby ProLogic sound, a satellite tuner and such. Generally, the electronics are based on a standard chassis that is also usedfor direct-view CRT television. Even the deflection circuits require minoradaptations at most. The high-voltage circuit is different because the EHT,focus and G2 voltages must be distributed over 3 CRTs. So this requires aspecial high-voltage part, which also includes an EHT capacitor and bleeder. There will be 3 CRT panels with video amplifiers. Because of the extremelyhigh brightness, projection tubes will burn the phosphor screen immediately infault conditions so a protection circuit is essential. And last but certainly not least, there is the dynamic convergence panel. Theheart is a waveform generator IC, often of a Japanese brand but nowadaysthere's also a digital variant by Philips. The old-fashioned way requires manymany potentiometers to program the waveforms. Then there's 5 or 6 convergenceamplifiers and a corresponding extra power supply. And usually this is wherethe single deflection circuits are distributed to the 3 CRTs. At the sametime the deflection currents are sensed for the protection circuits. Designing a PTV from a DVTV requires several man-years of work. In thefactory, a special corner is devoted to the assembly. There you'll findspecially educated people and the speed of the assembly line is a lot lowerthan usual. It requires many more adjustments, e.g. 3 optical and 3 electricalfocus adjustments and then convergence. For more information on TV technology:------------------------------------- The books listed in the section: "Suggested references" include additionalinformation on the theory and implementation of the technology of televisionstandards and TV receivers. For an on line introduction to TV and monitor technology, check out thePhilips/Magnavox Electronics Reference WEB site. There you will findlinks to a number of articles on the basic principles of operation of CDplayers, laserdisc and optical drives, TVs, VCRs, camcorders, loudspeakers,satellite receivers, and other consumer A/V equipment. The Video Handbookalso includes descriptions of video signals and common video connectors. On-line tech-tips databases:--------------------------- A number of organizations have compiled databases covering thousands of commonproblems with VCRs, TVs, computer monitors, and other electronics equipment.Most charge for their information but a few, accessible via the Internet, areeither free or have a very minimal monthly or per-case fee. In other cases, alimited but still useful subset of the for-fee database is freely available. A tech-tips database is a collection of problems and solutions accumulated bythe organization providing the information or other sources based on actualrepair experiences and case histories. Since the identical failures oftenoccur at some point in a large percentage of a given model or product line,checking out a tech-tips database may quickly identify your problem andsolution. In that case, you can greatly simplify your troubleshooting or at leastconfirm a diagnosis before ordering parts. My only reservation with respectto tech-tips databases in general - this has nothing to do with any one inparticular - is that symptoms can sometimes be deceiving and a solution thatworks in one instance may not apply to your specific problem. Therefore,an understanding of the hows and whys of the equipment along with some goodold fashioned testing is highly desirable to minimize the risk of replacingparts that turn out not to be bad. The other disadvantage - at least from one point of view - is that you do notlearn much by just following a procedure developed by others. There is noexplanation of how the original diagnosis was determined or what may havecaused the failure in the first place. Nor is there likely to be any listof other components that may have been affected by overstress and may failin the future. Replacing Q701 and C725 may get your equipment going againbut this will not help you to repair a different model in the future. Having said that, here are three tech-tips sites for computer monitors, TVs,and VCRs: * http://www.anatekcorp.com/techforum.htm (currently free).* http://www.repairworld.com/ ($8/month).* http://elmswood.guernsey.net/ (Free, very limited).* http://ramiga.rnet.cgl.com/electronics/info.html (free large text files). This one has quite a bit of info for just TVs (at present): * http://home.inreach.com/ba501/Tech_Tip_Page.htm These types of sites seem to come and go so it is worth checking them out fromtime-to-time even if you don't have a pressing need. If possible, downloadand archive any useful information for use on a rainy day in the future. **************** CRT Basics **************** Note: Most of the information on TV and monitor CRT construction, operation,interference and other problems. has been moved to the document: "TV andMonitor CRT (Picture Tube) Information". The following is just a briefintroduction with instructions on degaussing. Color CRTs - shadow masks and aperture grills:--------------------------------------------- All color CRTs utilize a shadow mask or aperture grill a fraction of aninch (1/2" typical) behind the phosphor screen to direct the electron beams for the red, green, and blue video signals to the proper phosphor dots.Since the electron beams for the R, G, and B phosphors originate fromslightly different positions (individual electron guns for each)and thus arrive at slightly different angles, only the proper phosphorsare excited when the purity is properly adjusted and the necessarymagnetic field free region is maintained inside the CRT. Note thatpurity determines that the correct video signal excites theproper color while convergence determines the geometricalignment of the 3 colors. Both are affected by magnetic fields.Bad purity results in mottled or incorrect colors. Bad convergenceresults in color fringing at edges of characters or graphics. The shadow mask consists of a thin steel or InVar (a ferrous alloy)with a fine array of holes - one for each trio of phosphordots - positioned about 1/2 inch behind the surface of the phosphorscreen. With most CRTs, the phosphors are arranged in triangularformations called triads with each of the color dots at the apexof the triangle. With many TVs and some monitors, they arearranged as vertical slots with the phosphors for the 3 colorsnext to one another. An aperture grille, used exclusively in Sony Trinitrons (and nowtheir clones as well), replaces the shadow mask with an array of finelytensioned vertical wires. Along with other characteristics of theaperture grille approach, this permits a somewhat higher possiblebrightness to be achieved and is more immune to other problems likeline induced moire and purity changes due to local heating causingdistortion of the shadow mask. However, there are some disadvantages of the aperture grille design: * weight - a heavy support structure must be provided for the tensioned wires (like a piano frame). * price (proportional to weight). * always a cylindrical screen (this may be considered an advantage depending on your preference. * visible stabilizing wires which may be objectionable or unacceptable for certain applications. Apparently, there is no known way around the need to keep the finewires from vibrating or changing position due to mechanical shockin high resolution tubes and thus all Trinitron monitors require1, 2, or 3 stabilizing wires (depending on tube size) across the screen which can be see as very fine lines on bright images. Somepeople find these wires to be objectionable and for some criticalapplications, they may be unacceptable (e.g., medical diagnosis). Degaussing (demagnetizing) a CRT:-------------------------------- Degaussing may be required if there are color purity problems with thedisplay. On rare occasions, there may be geometric distortion causedby magnetic fields as well without color problems. The CRT can getmagnetized: * if the TV or monitor is moved or even just rotated. * if there has been a lightning strike nearby. A friend of mine had a lightning strike near his house which produced all of the effects of the EMP from a nuclear bomb. * If a permanent magnet was brought near the screen (e.g., kid's magnet or megawatt stereo speakers). * If some piece of electrical or electronic equipment with unshielded magnetic fields is in the vicinity of the TV or monitor. Degaussing should be the first thing attempted whenever colorpurity problems are detected. As noted below, first try theinternal degauss circuits of the TV or monitor by power cycling a fewtimes (on for a minute, off for 30 minutes, on for a minute, etc.)If this does not help or does not completely cure the problem,then you can try manually degaussing. Commercial CRT Degaussers are available from parts distributorslike MCM Electronics and consist of a hundred or so turns of magnet wirein a 6-12 inch coil. They include a line cord and momentary switch. You flip on the switch, and bring the coil to within several inches of the screen face. Then you slowly draw the center of the coil toward one edge of the screen and trace the perimeter of the screen face. Then return to the original position of the coil being flat against the center of the screen. Next, slowly decrease the field to zero by backing straight up across the room as you hold the coil. When you are farther than 5 feet away you can release the line switch. The key word here is ** slow **. Go too fast and you will freeze theinstantaneous intensity of the 50/60 Hz AC magnetic field variationinto the ferrous components of the CRT and may make the problem worse. It looks really cool to do this while the CRT is powered. The kids willlove the color effects. Bulk tape erasers, tape head degaussers, open frame transformers, and the"ass-end" of a weller soldering gun can be used as CRT demagnetizers butit just takes a little longer. (Be careful not to scratch the screenface with anything sharp.) It is imperative to have the CRT running whenusing these whimpier approaches, so that you can see where there are still impurities. Never release the power switch until you're 4 or 5 feet away from the screen or you'll have to start over. I've never known of anything being damaged by excess manual degaussingthough I would recommend keeping really powerful bulk tape erasers turneddegaussers a couple of inches from the CRT. If an AC degaussing coil or substitute is unavailable, I have even donedegaussed with a permanent magnet but this is not recommended since it is morelikely to make the problem worse than better. However, if the displayis unusable as is, then using a small magnet can do no harm. (Don't usea 20 pound speaker or magnetron magnet as you may rip the shadow mask rightout of the CRT - well at least distort it beyond repair. What I have inmind is something about as powerful as a refrigerator magnet.) Keep degaussing fields away from magnetic media. It is a good idea toavoid degaussing in a room with floppies or back-up tapes. When removingmedia from a room remember to check desk drawers and manuals for strayfloppies, too. It is unlikely that you could actually affect magnetic media but bettersafe than sorry. Of the devices mentioned above, only a bulk eraser orstrong permanent magnet are likely to have any effect - and then only whenat extremely close range (direct contact with media container). All color CRTs include a built-in degaussing coil wrapped around the perimeter of the CRT face. These are activated each time the CRT is powered up cold by a 3 terminal thermister device or other controlcircuitry. This is why it is often suggested that color purity problemsmay go away "in a few days". It isn't a matter of time; it's the numberof cold power ups that causes it. It takes about 15 minutes of the powerbeing off for each cool down cycle. These built-in coils with thermalcontrol are never as effective as external coils. See the document: " TV and Monitor CRT (Picture Tube) Information" forsome additional discussion of degaussing tools, techniques, and cautions. ******** TV Placement And Preventive Maintenance ******** General TV placement considerations:----------------------------------- Proper care of a TV does not require much. Following the recommendationsbelow will assure long life and minimize repairs: * Subdued lighting is preferred for best viewing conditions but I will not attempt to tell you how to arrange your room! * Locate the TV away from extremes of hot and cold. Avoid damp or dusty locations if possible. (Right you say, keep dreaming!) * Allow adequate ventilation - TVs use more power than any of your other A/V components. Heat buildup takes its toll on electronic components. Leave at least 3 inches on top and sides for air circulation if the entertainment center does not have a wide open back panel. Do not pile other components like VCRs on top of the TV if possible (see below). * Do not put anything on top of the TV that might block the ventilation grill in the rear or top of the cover. This is the major avenue for the convection needed to cool internal components. * If possible, locate the VCR away from the TV. Some VCRs are particularly sensitive to interference from the TV's circuitry and while this won't usually damage anything, it may make for less than optimal performance due to RF interference. The reverse is sometimes true as well. In addition, modern VCRs are NOT built like the Brooklyn Bridge! The weight of a TV or stereo components could affect the VCR mechanically, messing up tape path alignment or worse. * If possible, locate your computer monitor away from the TV. Interaction of the electromagnetic fields of the deflection systems may result in one or both displays jiggling, wiggling, or vibrating. * Locate loudspeakers and other sources of magnetic fields at least a couple of feet from the TV. This will minimize the possibility of color purity or geometry problems. * Make sure all input-output video and audio connections are tight and secure to minimize intermittent or noisy pictures and sound. Use proper high quality cable only long enough to make connections conveniently. * Finally, store video cassettes well away from all electronic equipment including and especially loudspeakers. Heat and magnetic fields will rapidly turn your priceless video collection into so much trash. The operation of the TV depends on magnetic fields for beam deflection. Enough said. Preventive maintenance:---------------------- Preventive maintenance for a TV is pretty simple - just keep the case cleanand free of obstructions. Clean the screen with a soft cloth just dampenedwith water and at most, mild detergent. DO NOT use anything so wet thatliquid may seep inside of the set around the edge of the picture tube - youcould end up with a very expensive repair bill when the liquid shorts outthe main circuit board lurking just below. If the set has a protectiveflat glass faceplate, there is usually an easy way (on newer sets with thistype of protection) of removing it to get at the inner face of the CRT. Cleanboth the CRT and the protective glass with a soft damp cloth and drythoroughly. If you have not cleaned the screen for quite a while, you will be amazed at the amount of black grime that collects due to the staticbuildup from the high voltage CRT supply. In really dusty situations, periodically vacuuming inside the case and the useof contact cleaner for the controls might be a good idea but realistically,you will not do this so don't worry about it. Warning about using a TV as a computer or video game display:------------------------------------------------------------ "I remember a while back (about 10 years) most home computers used to hook up to televisions. I seem to remember them having some effect on the TV though. I think they made the TV go blurry after a while. I was just wondering what these computers used to do to the televisions to mess them up like that. I thought a TV signal was a TV signal." The problem was screen burn. Since computers of that ear were mostly textand video games tended to use fixed patterns for scenery, patterns tendedto be burned into the phosphor such that they were noticeably darker andless sensitive in those areas. This was exacerbated by the tendency torun them devices at very high brightness levels. Modern computers and video games should not be nearly as much of a risk sincethe displays are so much more varied and dynamic. Nevertheless, setting thebrightness at a moderate level would be prudent. ************** TV Troubleshooting ************** SAFETY:------ TVs and computer or video monitors are among the more dangerous of consumerelectronics equipment when it comes to servicing. (Microwave ovens areprobably the most hazardous due to high voltage at high power.) There are two areas which have particularly nasty electrical dangers: thenon-isolated line power supply and the CRT high voltage. Major parts of nearly all modern TVs and many computer monitors are directlyconnected to the AC line - there is no power transformer to provide theessential barrier for safety and to minimize the risk of equipment damage.In the majority of designs, the live parts of the TV or monitor are limitedto the AC input and line filter, degauss circuit, bridge rectifier and mainfilter capacitor(s), low voltage (B+) regulator (if any), horizontal outputtransistor and primary side of the flyback (LOPT) transformer, and partsof the startup circuit and standby power supply. The flyback generates mostof the other voltages used in the unit and provides an isolation barrier sothat the signal circuits are not line connected and safer. Since a bridge rectifier is generally used in the power supply, bothdirections of the polarized plug result in dangerous conditions and anisolation transformer really should be used - to protect you, your testequipment, and the TV, from serious damage. Some TVs do not have anyisolation barrier whatsoever - the entire chassis is live. These areparticularly nasty. The high voltage to the CRT, while 200 times greater than the line input,is not nearly as dangerous for several reasons. First, it is present in avery limited area of the TV or monitor - from the output of the flybackto the CRT anode via the fat red wire and suction cup connector. If youdon't need to remove the mainboard or replace the flyback or CRT, thenleave it alone and it should not bite. Furthermore, while the shock fromthe HV can be quite painful due to the capacitance of the CRT envelope, itis not nearly as likely to be lethal since the current available from theline connected power supply is much greater. Safety guidelines:----------------- These guidelines are to protect you from potentially deadly electrical shockhazards as well as the equipment from accidental damage. Note that the danger to you is not only in your body providing a conductingpath, particularly through your heart. Any involuntary muscle contractionscaused by a shock, while perhaps harmless in themselves, may cause collateraldamage - there are many sharp edges inside this type of equipment as well asother electrically live parts you may contact accidentally. The purpose of this set of guidelines is not to frighten you but rather tomake you aware of the appropriate precautions. Repair of TVs, monitors,microwave ovens, and other consumer and industrial equipment can be bothrewarding and economical. Just be sure that it is also safe! * Don't work alone - in the event of an emergency another person's presence may be essential. * Always keep one hand in your pocket when anywhere around a powered line-connected or high voltage system. * Wear rubber bottom shoes or sneakers. * Don't wear any jewelry or other articles that could accidentally contact circuitry and conduct current, or get caught in moving parts. * Set up your work area away from possible grounds that you may accidentally contact. * Know your equipment: TVs and monitors may use parts of the metal chassis as ground return yet the chassis may be electrically live with respect to the earth ground of the AC line. Microwave ovens use the chassis as ground return for the high voltage. In addition, do not assume that the chassis is a suitable ground for your test equipment! * If circuit boards need to be removed from their mountings, put insulating material between the boards and anything they may short to. Hold them in place with string or electrical tape. Prop them up with insulation sticks - plastic or wood. * If you need to probe, solder, or otherwise touch circuits with power off, discharge (across) large power supply filter capacitors with a 2 W or greater resistor of 100 to 500 ohms/V approximate value (e.g., for a 200 V capacitor, use a 20K to 100K ohm resistor). Monitor while discharging and verify that there is no residual charge with a suitable voltmeter. In a TV or monitor, if you are removing the high voltage connection to the CRT (to replace the flyback transformer for example) first discharge the CRT contact (under the insulating cup at the end of the fat red wire). Use a 1M to 10M ohm 5 W or greater wattage (for its voltage holdoff capability, not power dissipation) resistor on the end of an insulating stick or the probe of a high voltage meter. Discharge to the metal frame which is connected to the outside of the CRT. * For TVs and monitors in particular, there is the additional danger of CRT implosion - take care not to bang the CRT envelope with your tools. An implosion will scatter shards of glass at high velocity in every direction. There are several tons of force attempting to crush the typical CRT. While implosion is not really likely even with modest abuse, why take chances? However, the CRT neck is relatively thin and fragile and breaking it would be very embarrassing and costly. Always wear eye protection when working around the back side of a CRT. * Connect/disconnect any test leads with the equipment unpowered and unplugged. Use clip leads or solder temporary wires to reach cramped locations or difficult to access locations. * If you must probe live, put electrical tape over all but the last 1/16" of the test probes to avoid the possibility of an accidental short which could cause damage to various components. Clip the reference end of the meter or scope to the appropriate ground return so that you need to only probe with one hand. * Perform as many tests as possible with power off and the equipment unplugged. For example, the semiconductors in the power supply section of a TV or monitor can be tested for short circuits with an ohmmeter. * Use an isolation transformer if there is any chance of contacting line connected circuits. A Variac(tm) is not an isolation transformer! The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea but will not protect you from shock from many points in a line connected TV or monitor, or the high voltage side of a microwave oven, for example. (Note however, that, a GFCI may nuisanse trip at power-on or at other random times due to leakage paths (like your scope probe ground) or the highly capacitive or inductive input characteristics of line powered equipment.) A fuse or circuit breaker is too slow and insensitive to provide any protection for you or in many cases, your equipment. However, these devices may save your scope probe ground wire should you accidentally connect it to a live chassis. * Don't attempt repair work when you are tired. Not only will you be more careless, but your primary diagnostic tool - deductive reasoning - will not be operating at full capacity. * Finally, never assume anything without checking it out for yourself! Don't take shortcuts! Troubleshooting tips:-------------------- Many problems have simple solutions. Don't immediately assume thatyour problem is some combination of esoteric complex convolutedfailures. For a TV, it may just be a bad connection or blown fuse. Rememberthat the problems with the most catastrophic impact on operation like a deadTV usually have the simplest solutions. The kind of problems we wouldlike to avoid at all costs are the ones that are intermittentor difficult to reproduce: the occasional interference or a TV thatrefuses to play 'StarTrek Voyager'. If you get stuck, sleep on it. Sometimes, just letting the problembounce around in your head will lead to a different more successfulapproach or solution. Don't work when you are really tired - it is bothdangerous (especially with respect to TVs) and mostly non-productive(or possibly destructive). Whenever working on precision equipment, make copious notes and diagrams.You will be eternally grateful when the time comes to reassemble the unit.Most connectors are keyed against incorrect insertion or interchangeof cables, but not always. Apparently identical screws may be of differinglengths or have slightly different thread types. Little parts may fit inmore than one place or orientation. Etc. Etc. Pill bottles, film canisters, and plastic ice cube trays come in handy forsorting and storing screws and other small parts after disassembly. Thisis particularly true if you have repairs on multiple pieces of equipmentunder way simultaneously. Select a work area which is wide open, well lighted, and where droppedparts can be located - not on a deep pile shag rug. The best location willalso be relatively dust free and allow you to suspend your troubleshootingto eat or sleep or think without having to pile everything into a cardboardbox for storage. Another consideration is ESD - Electro-Static Discharge. Some components(like ICs) in a TV are vulnerable to ESD. There is no need to go overboardbut taking reasonable precautions such as getting into the habit of touchinga **safe** ground point first. WARNING: even with an isolation transformer, a live chassis should **not** beconsidered a safe ground point. When the set is unplugged, the tuner shieldor other signal ground points should be safe and effective. A basic set of precision hand tools will be all you need to disassemblea TV and perform most adjustments. These do not need to be reallyexpensive but poor quality tools are worse than useless and can causedamage. Needed tools include a selection of Philips and straight bladescrewdrivers, socket drivers, needlenose pliers, wire cutters, tweezers,and dental picks. For adjustments, a miniature (1/16" blade) screwdriverwith a non-metallic tip is desirable both to prevent the presence ofmetal from altering the electrical properties of the circuit and tominimize the possibility of shorting something from accidental contactwith the circuitry. A set of plastic alignment tools will be useful formaking adjustments to coils and RF transformers. A low power (e.g., 25 W) fine tip soldering iron and fine rosin core solderwill be needed if you should need to disconnect any soldered wires (on purposeor by accident) or replace soldered components. A higher power iron or smallsoldering gun will be needed for dealing with larger components. CAUTION: You can easily turn a simple repair (e.g., bad solder connections)into an expensive mess if you use inappropriate soldering equipment and/orlack the soldering skills to go along with it. If in doubt, find someone elseto do the soldering or at least practice, practice, practice, soldering anddesoldering on a junk circuit board first! See the document: "Troubleshootingand Repair of Consumer Electronics Equipment" for additional info on solderingand rework techniques. For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller'(they are the same) and a heat gun or blow dryer come in handy to identifycomponents whose characteristics may be drifting with temperature. Using theextension tube of the spray can or making a cardboard nozzle for the heatgun can provide very precise control of which components you are affecting. For info on useful chemicals, adhesives, and lubricants, see "Repair Briefs,an Introduction" as well as other documents available at this site. Test equipment:-------------- Don't start with the electronic test equipment, start with some analyticalthinking. Your powers of observation (and a little experience) will makea good start. Your built in senses and that stuff betweenyour ears represents the most important test equipment you have. However, some test equipment will be needed: * Multitester (DMM or VOM) - This is essential for checking of power supply voltages and voltages on the pins of ICs or other components - service literature like the Sams' Photofacts described elsewhere in this document include voltage measurements at nearly every circuit tie point for properly functioning equipment. The multitester will also be used to check components like transistors, resistors, and capacitors for correct value and for shorts or opens. You do not need a fancy instrument. A basic DMM - as long as it is reliable - will suffice for most troubleshooting. If you want one that will last for many years, go with a Fluke. However, even the mid range DMMs from Radio Shack have proven to be reliable and of acceptable accuracy. For some kinds of measurements - to deduce trends for example - an analog VOM is preferred (though some DMMs have a bar graph scale which almost as good). * Oscilloscope - While many problems can be dealt with using just a multimeter, a 'scope will be essential as you get more into advanced troubleshooting. Basic requirements are: dual trace, 10-20 MHz minimum vertical bandwidth, delayed sweep desirable but not essential. A good set of proper 10x/1x probes. Higher vertical bandwidth is desirable but most consumer electronics work can be done with a 10 MHz scope. A storage scope or digital scope might be desirable for certain tasks but is by no means essential for basic troubleshooting. I would recommend a good used Tektronix or HP scope over a new scope of almost any other brand. You will usually get more scope for your money and these things last almost forever. My 'good' scope is the militarized version (AN/USM-281A) of the HP180 lab scope. This has a dual channel 50 MHz vertical plugin and a delayed sweep horizontal plugin. I have seen these going for under $300 from surplus outfits. For a little more money, you can get a Tek 465 100 Mhz scope ($400-700) which will suffice for all but the most demanding (read: RF or high speed digital) repairs. * A video signal source - both RF and baseband (RCA jacks). Unless you are troubleshooting tuner or video/audio input problems, either one will suffice. RF sources include a pair of rabbit ears or an outdoor antenna, a cable connection, or a VCR with a working RF modulator. This will be more convenient than an antenna connection and will permit you to control the program material. In fact, making some test tapes using a camcorder or video camera to record static test patterns will allow you full control of what is being displayed and for how long. * Color bar/dot/crosshatch signal generator. This is a useful piece of equipment if you are doing a lot of TV or monitor repair and need to perform CRT convergence and chroma adjustments. However, there are alternatives that are almost as good: a VHS recording of these test patterns will work for TVs. A PC programmed to output a suitable set of test patterns will be fine for monitors (and TVs if you can set up the video card to produce an NTSC/PAL signal. This can be put through a VCR to generate the RF (Channel 3/4) input to your TV if it does not have direct video inputs (RCA jacks). Incredibly Handy widgets:------------------------ These are the little gadgets and homemade testers that are useful for manyrepair situations. Here are just a few of the most basic: * Series light bulb for current limiting during the testing of TVs, monitors, switching power supplies, audio power amplifiers, etc. I built a dual outlet box with the outlets wired in series so that a lamp can be plugged into one outlet and the device under test into the other. For added versatility, add a regular outlet and 'kill' switch using a quad box instead. The use of a series load will prevent your expensive replacement part like a horizontal output transistor from blowing if there is still some fault in the circuit you have failed to locate. * A Variac. It doesn't need to be large - a 2 A Variac mounted with a switch, outlet and fuse will suffice for most tasks. However, a 5 amp or larger Variac is desirable. If you will be troubleshooting 220 VAC equipment in the US, there are Variacs that will output 0-240 VAC from a 115 VAC line (just make sure you don't forget that this can easily fry your 115 VAC equipment.) By varying the line voltage, not only can you bring up a newly repaired TV gradually to make sure there are no problems but you can also evaluate behavior at low and high line voltage. This can greatly aid in troubleshooting power supply problems. Warning: a Variac is not an isolation transformer and does not help with respect to safety. You need an isolation transformer as well. * Isolation transformer. This is very important for safely working on live chassis equipment. Since all modern TVs use a line connected power supply, it is essential. You can build one from a pair of similar power transformers back-to-back (with their highest rated secondaries connected together. I built mine from a couple of similar old tube type TV power transformers mounted on a board with an outlet box including a fuse. Their high voltage windings were connected together. The unused low voltage windings can be put in series with the primary or output windings to adjust voltage. Alternatively, commercial line isolation transformers suitable for TV troubleshooting are available for less than $100 - well worth every penny. * Variable isolation transformer. You don't need to buy a fancy combination unit. A Variac can be followed by a normal isolation transformer. (The opposite order also works. There may be some subtle differences in load capacity.). * Degaussing coil. Make or buy. The internal degaussing coil salvaged from a defunct TV doubled over to half it original diameter to increase its strength in series with a 200 W light bulb for current limiting will work just fine. Or, buy one from a place like MCM Electronics - about $15 for one suitable for all but the largest TVs. Also, see the section: "Degaussing (demagnetizing) a CRT". Safe discharging of capacitors in TVs and video monitors:-------------------------------------------------------- It is essential - for your safety and to prevent damage to the device undertest as well as your test equipment - that large or high voltage capacitorsbe fully discharged before measurements are made, soldering is attempted,or the circuitry is touched in any way. Some of the large filter capacitorscommonly found in line operated equipment store a potentially lethal charge. This doesn't mean that every one of the 250 capacitors in your TV need to bedischarged every time you power off and want to make a measurement. However,the large main filter capacitors and other capacitors in the power suppliesshould be checked and discharged if any significant voltage is found afterpowering off (or before any testing - some capacitors (like the high voltageof the CRT in a TV or video monitor) will retain a dangerous or at leastpainful charge for days or longer!) The technique I recommend is to use a high wattage resistor of about100 ohms/V of the working voltage of the capacitor. This willprevent the arc-welding associated with screwdriver discharge but willhave a short enough time constant so that the capacitor will drop toa low voltage in at most a few seconds (dependent of course on theRC time constant and its original voltage). Then check with a voltmeter to be double sure. Better yet, monitorwhile discharging (not needed for the CRT - discharge is nearlyinstantaneous even with multi-M ohm resistor). Obviously, make sure that you are well insulated! * For the main capacitors in a switching power supply which might be 100 uF at 350 V this would mean a 5K 10W resistor. RC=.5 second. 5RC=2.5 seconds. A lower wattage resistor can be used since the total energy in not that great. The circuit described below can used to provide a visual indication of polarity and charge. * For the CRT, use a high wattage (not for power but to hold off the high voltage which could jump across a tiny 1/4 watt job) resistor of a few M ohms discharged to the chassis ground connected to the outside of the CRT - NOT SIGNAL GROUND ON THE MAIN BOARD as you may damage sensitive circuitry. The time constant is very short - a ms or so. However, repeat a few times to be sure. (Using a shorting clip lead may not be a bad idea as well while working on the equipment - there have been too many stories of painful experiences from charge developing for whatever reasons ready to bite when the HV lead is reconnected.) Note that if you are touching the little board on the neck of the CRT, you may want to discharge the HV even if you are not disconnecting the fat red wire - the focus and screen (G2) voltages on that board are derived from the CRT HV. WARNING: Most common resistors - even 5 W jobs - are rated for only a few hundred volts and are not suitable for the 25KV or more found in modern TVs and monitors. Alternatives to a long string of regular resistors are a high voltage probe or a known good focus/screen divider network. However, note that the discharge time constant with these may be a few seconds. Also see the section: "Additional information on discharging CRTs". If you are not going to be removing the CRT anode connection, replacing the flyback, or going near the components on the little board on the neck of the CRT, I would just stay away from the fat red wire and what it is connected to including the focus and screen wires. Repeatedly shoving a screwdriver under the anode cap risks scratching the CRT envelope which is something you really do not want to do. Again, always double check with a reliable voltmeter! Reasons to use a resistor and not a screwdriver to discharge capacitors: 1. It will not destroy screwdrivers and capacitor terminals. 2. It will not damage the capacitor (due to the current pulse). 3. It will reduce your spouse's stress level in not having to hear those scary snaps and crackles. Additional information on discharging CRTs:------------------------------------------ You may hear that it is only safe to discharge from the Ultor to the Dag.So, what the @#$% are they talking about? :-). (From: Asimov (mike.ross@juxta.mnet.pubnix.ten)). 'Dag' is short for Aquadag. It is a type of paint made of a graphite pigmentwhich is conductive. It is painted onto the inside and outside of picturetubes to form the 2 plates of a high voltage filter capacitor using the glassin between as dielectric. This capacitor is between .005uF and .01uF invalue. This seems like very little capacity but it can store a substantialcharge with 25,000 volts applied. The outside "dag" is always connected to the circuit chassis ground via aseries of springs, clips, and wires around the picture tube. The high voltageor "Ultor" terminal must be discharged to chassis ground before working on thecircuit especially with older TV's which didn't use a voltage divider toderive the focus potential or newer TV's with a defective open divider. For more details, see the document: "TV and Monitor CRT (Picture Tube)Information. Safe troubleshooting techniques for line powered TVs:---------------------------------------------------- TVs are particularly dangerous with respect to troubleshooting due to the factthat a substantial portion of their circuitry - sometimes all of it - isdirectly line connected. Even if your are working in a totally unrelatedarea like the sound circuits, awareness of the general design and locationof the line-connected circuits can prove to be a life saver. These designs may take several forms: 1. Separate switchmode power supply (SMPS). In this case, only the primary side of the power supply is line connected. The remainder of the TV is usually isolated from the line by the high frequency transformer and feedback device (transformer or optoisolator) of the switchmode power supply. 2. On-board SMPS - a portion of the circuitry on the mainboard is directly line-connected. In the best case, this is restricted to the area around the power cord connections and well marked on both top and bottom but don't count on it. Again, the rest of the TV may be isolated but avoiding hazardous areas is more difficult especially in cramped quarters. 3. Flyback derived power supply - a non-isolated linear (usually) power supply provides B+ to the horizontal deflection (and startup circuit). All other system power is derived from secondary windings on the flyback transformer. Similar comments to (2) above apply. (1) to (3) may be found in TVs with A/V inputs and outputs. 4. Full hot chassis - a bridge rectifier/filter capacitor/linear regulator provides some voltages including B+. The flyback secondaries provide the remaining voltages. All share a common return which is at the intersection of two of the diodes of the bridge rectifier. There is no isolation. This type of design will usually not be found in a TV where there are external connections (other than the RF antenna/cable connector which can be capacitively isolated and you may actually get an AC reading or even sparks between the RF shield and an earth ground due to this capacitance.) WARNING: Never attempt to add A/V inputs or outputs to such a TV as the signals and shields will be electrically live. However, some TVs with A/V inputs/outputs actually had a live chassis and used an isolated means of coupling the signals from/to the external jacks: (From: Bill Coffel (bc@datamix.com)). The late 70's and early 80's Sony CVM 1250/1750/2150 (12"/17"/21") monitors (TV) have a HOT chassis. In fact they are KV-1201/1701/2101 TV sets in larger cabinet With a 3 prong plug!!!! The inputs and outputs are isolated via opto couplers and transformers on an additional circuit board (about 6" by 8" and powered by a small transformer) the connector panel is the only part grounded via the third prong. If someone thinks its not a live chassis they are in for quite a shock. Always use an isolation transformer, whatever kind of design is used in theequipment you are troubleshooting. There are very few situations in whichan isolation transformer will hurt. If you use it automatically, you willnever have a chance to screw up. Identify the appropriate ground point (return) for your multimeter or scope.These should be marked in the Sams' Photofact or service manual. There maybe several such returns such as: non-isolated, signal, and CRT. Selectingthe wrong one - even momentarily connecting to it - can ruin your whole day. If you are not using an isolation transformer (a no-no), connecting yourscope to the wrong ground point can result in (1) blown fuses and/or blownparts, and a very dangerous situation and (2) readings that don't make sensegenerally with distorted power line frequency signals of high amplitude. * Use the non-isolated ground (A) (with your isolation transformer on the TV *only* for measurements of voltage on the line-connected power supply. * Use the signal ground (B) for all measurements of tuner, IF, video, and sound circuits. Whenever you get a reading or waveform that is grossly wrong, confirm thatyou are using the proper ground point! Note that failures of fusableresistors in the *return* of the HOT or power supply chopper or elsewherecan also result in points that should be near ground floating at unexpectedvoltage levels. The general arrangement of components for a typical TV using a linear B+supply with isolated auxiliary supplies for the signal circuits is shownbelow including the (linear) line-connected power supply, horizontaldeflection output (drive, horizontal output transistor, flyback), anda typical Aux power supply output. Line fuse Main bridge Part of flyback _ rectifier +----------+ B+ transformer H o--_ --+------>---+--- -----------------+ : Aux 1 Filter, ): +-->--+--o +--->---+ REG, etc. ):( __ 115 VAC ):( --- +----- N o---------+--- G - Power line earth ground /// ( \ E Output Signal via building wiring ^ ( Transistor ground +------+ (HOT) ' A __ Non-isolated return --> /// (connected points) For this power supply, what if?: 1. You connect your scope ground clip to the non-isolated ground (A) and you are *not* using an isolation transformer? Answer: you blow the line fuse and/or melt your scope probe ground lead. Other parts may be damaged as well. In effect, you have just shorted across the bottom diode of the bridge. 2. You attempt to monitor a video signal with your scope ground connected to the non-isolated ground (A)? Answer: you see only a highly distorted power line waveform of roughly 100 V p-p In effect, you are measuring across one of the diodes of the bridge rectifier, stray capacitance, etc. The series light bulb trick:--------------------------- When powering up a TV (or any other modern electronic devices with expensivepower semiconductors) that has had work done on any power circuits, it isdesirable to minimize the chance of blowing your newly installed parts shouldthere still be a fault. There are two ways of doing this: use of a Variac tobring up the AC line voltage gradually and the use of a series load to limitcurrent to power semiconductors. Actually using a series load - a light bulb is just a readily available cheapload - is better than a Variac (well both might be better still) since it willlimit current to (hopefully) non-destructive levels. What you want to do is limit current to the critical parts - usually thehorizontal output transistor (HOT). Most of the time you will get away withputting it in series with the AC line. However, sometimes, putting a lightbulb directly in the B+ circuit will provide better protection as it willlimit the current out of the main filter capacitors to the HOT. Actually,an actual power resistor is probably better as its resistance is constantas opposed to a light bulb which will vary by 1:10 from cold to hot. Thelight bulb, however, provides a nice visual indication of the current drawnby the circuit under test. For example: * Full brightness: short circuit or extremely heavy load - a fault probably is still present. * Initially bright but then settles at reduced brightness: filter capacitors charge, then lower current to rest of circuit. This is what is expected when the equipment is operating normally. There could still be a problem with the power circuits but it will probably not result in an immediate catastrophic failure. * Pulsating: power supply is trying to come up but shutting down due to overcurrent or overvoltage condition. This could be due to a continuing fault or the light bulb may be too small for the equipment. Note: for a TV or monitor, it may be necessary (and desirable) to unplug thedegauss coil as this represents a heavy initial load which may prevent the unitfrom starting up with the light bulb in the circuit. The following are suggested starting wattages: * 40 W bulb for VCR or laptop computer switching power supplies.* 100 W bulb for small (i.e., B/W or 13 inch color) TVs.* 150-200 W bulb for large color or projection TVs. A 50/100/150 W (or similar) 3-way bulb in an appropriate socket comes inhandy for this but mark the switch so that you know which setting is which! Depending on the power rating of the equipment, these wattages may need to beincreased. However, start low. If the bulb lights at full brightness, youknow there is still a major fault. If it flickers or the TV (or other device)does not quite come fully up, then it should be safe to go to a larger bulb.Resist the temptation to immediately remove the bulb at this point - I havebeen screwed by doing this. Try a larger one first. The behavior shouldimprove. If it does not, there is still a fault present. Note that some TVs and monitors simply will not power up at all with any kindof series load - at least not with one small enough (in terms of wattage) toprovide any real protection. The microcontroller apparently senses the dropin voltage and shuts the unit down or continuously cycles power. Fortunately,these seem to be the exceptions. Getting inside a TV:------------------- You will void the warranty - at least in principle. There are usually nowarranty seals on a TV so unless you cause visible damage or mangle thescrews, it is unlikely that this would be detected. You need to decide.A TV still under warranty should probably be returned for warrantyservice for any covered problems except those with the most obviousand easy solutions. Another advantage of using warranty service is thatshould your problem actually be covered by a design change, this will beperformed free of charge. And, you cannot generally fix a problem whichis due to poor design! Getting into a TV is usually quite simple requiring the removal of anywherefrom 4 to 16 Philips or 1/4" hex head screws - most around the rear edge of thecabinet or underneath, a couple perhaps in the middle. Disconnect the antennaand/or antenna or cable wiring first as it may stay with catch on the rearcover you are detaching. Reconnect whatever is needed for testing after thecover is removed. As you pull the cover straight back (usually) and off, make sure that noother wires are still attached. Often, the main circuit board rests onthe bottom of the cover in some slots. Go slow as this circuit board maytry to come along with the back. Once the back is off, you may need to propthe circuit board up with a block of wood to prevent stress damage and contactwith the work surface. Most TVs can still be positioned stably on any of three sides (left, right,bottom) even without the rear cover. However, some require the cover formechanical strength or to not easily fall over. Be careful- larger TVs,in particular, are quite heavy and bulky. Get someone to help and takeprecautions if yours is one of the unstable variety. If need be, the setcan usually safely be positioned on the CRT face if it is supported byfoam or a folded blanket. Reassemble in reverse order. Getting the circuit board to slide smoothlyinto its slots may take a couple of attempts but otherwise there shouldbe no surprises. Specific considerations before poking around inside a TV:-------------------------------------------------------- Specific considerations before poking around inside a TV or monitor:------------------------------------------------------------------- Both electrical and mechanical dangers lurk: * Main filter capacitor(s). This is the most dangerous (not the HV as you would expect). Fortunately, these capacitors will normally discharge in a few minutes or less especially if the unit is basically working as the load will normally discharge the capacitors nearly fully as power is turned off. With TVs, the main filter capacitor is nearly always on the mainboard. Monitors are more likely to have a separate power supply module. However, you should check across this capacitor - usually only one and by far the largest in the set - with a voltmeter and discharge as suggested in the section: "Safe discharging of capacitors in TVs and video monitors" if it holds more than a few volts (or wait longer) before touching anything. Some of these are as large as 1,000 uF charged to 160 V - about 13 w-s or a similar amount of energy as that stored in an electronic flash. This is enough to be potentially lethal under the wrong circumstances. * High Voltage capacitor formed by the envelope of the CRT. It is connected to the flyback transformer by the fat (usually red) wire at the suction cup (well, it looks like one anyhow) attached to the CRT. This capacitor can hold a charge for quite a while - weeks in the case of an old tube type TV! If you want to be doubly sure, discharge this also. However, unless you are going to be removing the HV connector/flyback, it should not bother you. The energy stored is about 1 w-s but if you touch it or come near to an exposed terminal, due to the high voltage, you will likely be handed *all* the energy and you *will* feel it. The danger is probably more in the collateral damage when you jump ripping flesh and smashing your head against the ceiling. Some people calibrate their jump based on voltage - about 1 inch/V. :-). There will be some HV on the back of the circuit board on the neck of the CRT but although you might receive a tingle but accidentally touching the focus or screen (G2) pins, it is not likely to be dangerous. * CRT implosion risk. Don't hammer on it. However, it is more likely that you will break the neck off the tube since the neck is relatively weak. This will ruin your whole day and the TV or monitor but will likely not result in flying glass everywhere. Just, don't go out of your way to find out. * Sharp sheet metal and so forth. This is not in itself dangerous but a reflex reaction can send your flesh into it with nasty consequences. Dusting out the inside of a TV:------------------------------ The first thing you will notice when you remove the cover is how superdusty everything is. Complements to the maid. You never dreamed therewas that much dust, dirt, and grime, in the entire house! Use a soft brush (like a new paintbrush) and a vacuum cleaner to carefullyremove the built up dust. Blowing off the dust will likely not hurt the TVunless it gets redeposited inside various controls or switches but willbe bad for your lungs - and will spread it all over the room. Don't turnanything - many critical adjustments masquerade as screws that just beg tobe tightened. Resist the impulse for being neat and tidy until you knowexactly what you are doing. Be especially careful around the components onthe neck of the CRT - picture tube - as some of these are easily shiftedin position and control the most dreaded of adjustments - for color purityand convergence. In particular, there will be a series of adjustable ringmagnets. It is a good idea to mark their position in any case withsome white paint, 'white out', or a Magic Marker so that if they do getmoved - or you move them deliberately, you will know where you started. Troubleshooting a TV with the mainboard disconnected:---------------------------------------------------- There are times when it is desirable to remove the chassis or mainboard andwork on it in a convenient location without having to worry about theequipment which will simulate the critical functions but this is rarelyan option for the doit-yourselfer. My approach is usually to do as much work as possible without removing themain board and not attempt to power it up when disconnected since there aretoo many unknowns. Professionals will plug the chassis into a piece ofequipment which will simulate the critical functions. Note that if you have a failure of the power supply - blown fuse, startup,etc., then it should be fine to disconnect the CRT since these problemsare usually totally unrelated. Tests should be valid. However, if you really want to do live testing with the main board removed,here are some considerations. There are usually several connections to theCRT and cabinet: * Deflection yoke - since the horizontal coils are part of the horizontal flyback circuit, there could be problems running without a yoke. This could be anything from it appearing totally dead to an overheating or blown horizontal output transistor. There may be no problems. Vertical and any convergence coils may or may not be problems as well. * CRT video Driver board - pulling this should not usually affect anything except possibly video output and bias voltages. * CRT 2nd anode - without the CRT, there will be no capacitor to filter the high voltage and you would certaily want to insulate the HV connector **real** well. I do not know whether there are cases where damage to flyback could result from running in thie manner, however. * Front panel controls - disconnecting these may result in inability to even turn the set on, erratic operation, and other unexpected behavior. * Degauss - you just won't have this function when disconnected. But who cares - you are not going to be looking at the screen anyhow. * Remote sensor - no remote control but I doubt that the floating signals will cause problems. * Speakers - there will be no audio but this should not cause damage. If you do disconnect everything, make sure to label any connectors whoselocation or orientation may be ambiguous. Most of the time, these willonly fit one way but not always. ****************** TV Adjustment ****************** User picture adjustment:----------------------- For general viewing, subdued lighting but not total darkness is probablybest. However, for most dramatic impact, a darkened environment may bepreferred. Make the following adjustments under the expected viewingconditions. Tune to a strong channel or play a good quality tape. Turn the brightness, contrast, and color controls all the way down. Centerthe tint control (NTSC, may not be present on PAL sets). Increase the brightness until a raster is just visible in the darkest(shadow) areas of the picture. Increase the contrast until the desired intensity of highlights is obtained. Since brightness and contrast are not always independent, go back and forthuntil you get the best picture. Initially adjust the color control for pastel shades rather than highlysaturated color. Set the tint control for best flesh tones. Then,increase the color control to obtain the desired degree of color saturation. Internal adjustments:-------------------- All of the service adjustments are accomplished either using controls insidethe set (mostly pots on the mainboard and CRT neck boards), or in most newerTVs, mostly via a service menu accessed from the remote or by using amanufacturer specific computer interface. * A Web site with some information on the general objectives of video and color setup procedures for both direct view and projection TVs is: - http://www.Tru-line.com/ (Tru-line Video Technologies) * Where actual pots are present, they may be labeled on the circuit boards or identified by a sticker on the TV's cover. Otherwise, the service manual or Sams' for the set will be required unless their function of the relevant pot is obvious. * For service menus accessed via the remote control, service information is almost a necessity since adjustment procedures vary widely and it is all too easy to totally mess things up - even to the point of inflicting serious and expensive damage to the set. For information on accessing the service menus if used on your model, see the section: "Setup adjustments lost - TV service codes". However, even if the access procedure is known, get the service manual or Sams'! * If a computer interface is required, you can most probably forget about attempting to adjust anything unless you find a friendly shop to provide the adapter and walk you through the procedure. Why would they want to do this? Because they know you there is a good chance that you will have to pay them to unscramble the mess you created! Focus adjustment:---------------- On a decent TV, you should be able to make out the individual scanninglines. If they are fuzzy, especially in bright areas, then focus may needto be adjusted. The focus pot is usually located on the flyback transformer or on anauxiliary panel nearby. Where there are two adjustment knobs on the flybacktransformer, the top one is generally for focus and the bottom one is for G2. The focus wire usually comes from the flyback orthe general area or from a terminal on a voltage the multiplier module(if used). It is usually a wire by itself going to the little boardon the neck of the CRT. Let the set warm up for at least half an hour. Display a good qualitysignal. Turn the user color control all the way down and the brightnessand contrast controls all the way up. This will be the worst case. Adjustthe focus control for best overall sharpness - you may not be able to get itperfect everywhere - center as well as corners. If best focus is at oneend of the focus pot's range and still not good enough, there may be aproblem in the focus divider, focus pot, or some related component. Adjustment of the internal SCREEN and color controls:---------------------------------------------------- The screen should be adjusted with a white pattern (snow from the tuner should do or turn the user COLOR control all the way down to get ablack and white picture). Put the set in Service mode (horizontal line)if it has such a switch in the back or inside. If not, just usethe raster in a darkened room. Adjust screen for a dim white line (raster). If the line is not white at its dimmest point, you willneed to adjust the drive and cutoff controls for R, G, & B. Alternatively, you can use the following procedure: Turn R, G, and B screen (or background) controls down. Now turn color control fully counterclockwise -- off. Now turn up red screen until the screen just shows a red hue. Now turn red gun down until red tint just goes away. Now do the same with the green and blue screen controls. Now adjust the two DRIVE controls for the best black and white picture. That`s all there is to it. I don`t like to work with just a thin "SETUP" line. Cartoons seem to be the best thing to have on while doing the above procedure. You can also use just plain snow (no program) if you prefer. If you can obtain a good b@w pic. when you`re done, the tube is good and the set if most likely functioning properly. Be patient and go slow while watching the large mirror that you are using during this procedure. (LEE) Optimal procedure for setting brightness/background and screen adjustments:-------------------------------------------------------------------------- For slight tweaks, the following is not necessary. However, if someoneturned all the internal controls or if you are making significant changesthat affect G2 (screen), then following the procedure below is desirableto achieve best performance and maximize life of the CRT. The typical user controls - brightness and contrast can, of course, be setarbitrarily, depending on video content and ambient lighting conditions. Set the user brightness and contrast controls in the middle for the followingadjustments and let the set warm up for 20 minutes or so. (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). Now the screen control, that's another matter. It sets the voltageon the second grid of the electron guns, typically between +500 and+1000 V. You will want to use a well-isolated screwdriver for thatif it is a naked potentiometer. In the old days there used to be 3separate potentiometers for 3 G2s, now there is generally only one. Its purpose is to set the cutoff voltage for the guns, i.e. thevoltage between K and G1 at which the beam is just off. The higheryou set the VG2, the higher VK - VG1 must be to cut off the beam. If you set VG2 too low then your picture will be dark. You cancompensate for that with the brightness control, which in effect willlower the VKs. A disadvantage is that you will not get optimumsharpness and peak brightness from your picture tube. If you set VG2 too high then your picture will be bright. You cancompensate for that with the brightness control, which in effect willraise the VKs. You might even get retrace lines which can usuallynot be made to disappear with the brightness control. Another disadvantage is that you will not get optimum LIFETIME from your picture tube. With a too high cutoff voltage the cathode (electron emitting surface) will wear out too soon. You will need to see the picture tube specifications (or possiblythe Sams' Photofact or service manual for the set --- sam) in order tofind the correct setting for the cutoff voltage. This is measuredas VK - VG1 (for each channel RGB) and is typically 130-160 V max.There will be spread between the 3 channels, typically the highestof the 3 measured values will be set against the upper limit. The usual adjustment procedure is as follows: * Use any low-level adjustments to set a black picture with all 3 cathode voltages at the specified level (e.g. 130 V) above the VG1 voltage (may be 0 V or 12 V or 20 V ?). (These are typically called RGB brightness, bias, or background level and are often on the little board on the neck of the CRT but not always --- sam). * Adjust VG2 (screen) until one colour just starts too light up, turn it back down until the screen is just black again. * Now adjust 2 of the 3 low-level black controls until the other 2 colours just light up, and then back to black again. * Select a white picture and use 2 low-level white (RGB drive or gain, also generally on the neck board --- sam) controls to set the proper colour temperature for white to your own taste. * Check your black calibration again, may have to iterate a bit. Color balance adjustment:------------------------ Color balance needs adjustment if the highlights and/or shadows of a blackand white picture (turn the color control all the way down) are not aperfectly neutral gray. Note: Some TV designs (Zenith uses this in a few models) automatically balanceCRT cathode drive by sensing emission from the red, green, and blue guns usinga gray scale reference pulse outside the viewable picture. If this is thecase with your set, there may be no user OR service adjustments :-(. A colorbalance problem in this case means either a failure of this circuitry or a CRTwhere the emission from the 3 cathodes is so unbalanced (usually due to onebeing much much weaker than the others) that compensation is not possible. To adjust the color balance: Turn the color control all the way down so thatyou get what should be a B/W picture. Set the user brightness and contrastcontrols about mid-range. The tint control should not matter (if it doesat this point, you have other chroma problems or an 'autocolor' switchis on limiting the range of some controls). Adjust the sub-brightness controls (may be called color screen, background,or the like) so that the dark areas of the picture are just visible andneutral gray. Then, adjust the color gain controls until the brightest areasare neutral white but not so bright that there is 'color bleeding' inthe highlights. This should get you close. If something is still shifting after warmup andget some cold-spray or even a little blower and try to locate the componentthat is drifting. Most likely a transistor or capacitor. Horizontal position, size, and linearity adjustment:--------------------------------------------------- Horizontal position may be set via a switch or jumper, a pot, or (mostlyin B/W TVs) a set of rings on the CRT neck. Horizontal size should be set so that there is about 10-15 percentoverscan left and right. This will allow ample margin for power linevoltage fluctuations, component aging, and the reduction in raster sizethat may occur with some VCR special effects (fast play) modes. Many sets no longer have any horizontal size adjustments and depend onaccurate regulation of the voltage to the horizontal output stageto control horizontal size. There may be a B+ adjustment to performfirst. On those that do, the adjustment may either be done by setting the B+voltage, by a pot, or a width coil in series with the horizontaldeflection coils. Modern sets do not generally have any linearity control but you may findthis on older models. You will need to go back and forth between sizeand linearity as these adjustments are usually not independent. Some of the newest sets control all these parameters via settings innon-volatile memory and use service menus accessed via the remote controlfor nearly all setup adjustments. Vertical position, size, and linearity adjustment:------------------------------------------------- Vertical position may be set via a switch or jumper, a pot, or (mostlyin B/W TVs) a set of rings on the CRT neck. Vertical size should be set so that there is about 10-15 percentoverscan top and bottom. This will allow ample margin for power linevoltage fluctuations, component aging, and the reduction in raster sizethat may occur with some VCR special effects (fast play) modes. Some sets no longer have any vertical size adjustments and depend onthe accurate regulation of the voltage to the vertical output stageto control vertical size. On those that do, the adjustment is usually a pot in the vertical outputcircuitry. If your set has a linearity control, you will need to adjustthis in conjunction with the size control as these are usually not independent. Some of the newest sets control all these parameters via settings innon-volatile memory and use service menus accessed via the remote controlfor nearly all setup. Pincushion adjustments:---------------------- There may be two controls - amplitude and phase. Pincushion amplitudeas its name implies, controls the size of the correction. Pincushionphase affects where on the sides it is applied. Don't expect perfection. If the controls have no effect, there is probably a fault in the pincushioncorrection circuitry. It is best to make these adjustments with a crosshatch or dot test pattern Geometry adjustment:------------------- This refers to imperfections in the shape of the picture not handledby the pincushion and size adjustments. These types of defects includetrapezoidal or keystone shaped raster and jogs or wiggles around the peripheryof the raster. Unfortunately, one way these are handled at the factory is toglue little magnets to strategic locations on the CRT and/or rotate littlemagnets mounted on the yoke frame. Unless you really cannot live with theway it is (assuming there isn't something actually broken), leave thesealone! You can end up with worse problems. In any case, carefully mark theposition AND orientation of every magnet so that if this happens, you canget back to where you started. If the magnets are on little swivels, someexperimenting with them one at a time may result in some improvement. Ofcourse, it is best to obtain a service manual and follow its instructions. Why is the convergence on my set bad near the edges:--------------------------------------------------- Very simple - nothing is quite perfect. Perfect convergence is noteven necessarily possible in theory with the set of adjustments availableon a typical TV. It is all a matter of compromises. Consider whatyou are trying to do: get three electron beams which originate fromdifferent electron guns to meet at a single point within a fractionof a mm everywhere on the screen. This while the beams are scanningat an effective writing rate of 20,000 mph across the face of a 27" CRTin a variable magnetic environment manufactured at a price you can affordwithout a second mortgage! CRT purity and convergence problems:----------------------------------- Purity assures that each of the beams for the 3 primary colors - red, green,and blue - strikes only the proper phosphor dots for that color. A totallyred scene will appear pure red and so forth. Symptoms of poor purity areblotches of discoloration on the screen. Objects will change shades of colorwhen the move from one part of the screen to another. Convergence refers to the control of the instantaneous positions of the red,green, and blue spots as they scan across the face of the CRT so that they areas nearly coincident as possible. Symptoms of poor convergence are coloredborders on solid objects or visible separate R, G, and B images of fine linesor images, Note: It is probably best to face the set East-West (front-to-back) whenperforming any purity and convergence adjustments. Since you probably do notknow what orientation will eventually be used, this is the best compromiseas the earth's magnetic field will be aligned mostly across the CRT. This willminimize the possible rotation of the picture when the unit is moved to itsfinal position but there may be a position shift. Neither of these is thatsignificant so it probably doesn't really matter that much unless you aresuper fussy. Of course, if you know the final orientation of the TV in yourentertainment center - and you don't expect to be redecorating, use thatinstead. Or, plan to do the final tilt and position adjustments after the setis in position - but this will probably require access to the inside! First, make sure no sources of strong magnetic fields are in the vicinity ofthe TV - loudspeakers, refrigerator magnets, MRI scanners, etc. A nearbylightning strike or EMP from a nuclear explosion can also affect purity. Cycle power a couple of times to degauss the CRT (1 minute on, 20 minutesoff) - see the section: "Degaussing (demagnetizing) a CRT". If the builtin degaussing circuits have no effect, use an external manual degaussing coil. Assuming this doesn't help, you will need to set the internal purityand/or convergence adjustments on the CRT. Modern CRTs usually use acombination of a series of magnetized moveable rings on the neck, and yokeposition and orientation to set purity and convergence. First, mark the positions of all adjustments - use white paint, 'White out',or a Magic Marker on the ring magnets on the neck of the CRT, the positionand tilt of the deflection yoke, and any other controls that you may touchdeliberately or by accident. However, if your set is still of the type with a drawer or panel of knobsfor these adjustments, don't even think about doing anything withouta service manual and follow it to the letter unless the functions of allthe knobs is clearly marked (some manufacturers actually do a pretty goodjob of this). Note: some CRTs do not have any adjustable rings for purity (and staticconvergence). Either an internal structure in the neck of the CRT or anexternal 'permalloy' sleeve is permanently magnetized at the factory andthere is not way of tweaking it in the field. However, it may be possibleto use a normal set of magnet rings in addition to or in place of it tocorrect for purity or convergence problems due to loss of magnetism dueto age or someone waving a 10 pound magnet near the CRT neck! CRT purity adjustment:--------------------- Purity on modern CRTs is usually set by a combination of a set of ringmagnets just behind the deflection yoke on the neck of the CRT and theposition of the yoke fore-aft. As always, mark the starting position ofall the rings and make sure you are adjusting the correct set if rings! Use the following purity adjustment procedure as a general guide only.Depending on the particular model TV, the following purity adjustmentprocedure may substitute green for red depending on the arrangement of theguns in the CRT. This description is based on the Sams' Photofact for the RCACTC111C chassis which uses a slot-mask CRT. The procedures for dot-maskand Trinitron (aperture grille) CRTs will vary slightly. See you servicemanual! Obtain a white raster (sometimes there is a test point that can be groundedto force this). Then, turn down the bias controls for blue and green sothat you have a pure red raster. Let the set warm up for a minimum of15 minutes. Loosen the deflection yoke clamp and move the yoke as far back as it will go, Adjust the purity magnets to center the red vertical raster on the screen. Move the yoke forward until you have the best overall red purity. Now, move the yoke forward until you have the best overall red purity.Tighten the clamp securely and reinstall the rubber wedges (if you sethas these) to stabilize the yoke position. Reset the video adjustmentsyou touched to get a red raster. CRT convergence adjustment:-------------------------- In the good old days when TVs were TVs (and not just a picture tube witha little circuit board attached) there were literally drawers full ofknobs for setting convergence. One could spend hours and still end upwith a less than satisfactory picture. As the technology progressed,the number of electronic adjustments went down drastically so that todaythere are very few if any. Unless you want a lot of frustration, I would recommend not messing withconvergence. You could end up a lot worse. I have no idea what is usedfor convergence on your set but convergence adjustments are neverquite independent of one another. You could find an adjustment thatfixes the problem you think you have only to discover some other areaof the screen is totally screwed. In addition, there are adjustmentsfor geometry and purity and maybe others that you may accidentally movewithout even knowing it until you have buttoned up the set. Warning: Accurately mark the original positions - sometimes you will changesomething that will not have an obvious effect but will be noticeablelater on. So it is extremely important to be able to get back to whereyou started. If only red/green vertical lines are offset, then it islikely that only a single ring needs to be moved - and by just a hair.But, you may accidentally move something else! If you really cannot live with it, make sure you mark everything verycarefully so you can get back to your current state. A service manual isessential! Convergence is set using a white crosshatch or dot test pattern. If youdo not have a test pattern generator, any static scene (from a camcorderor previously recorded tape, for example) with a lot of fine detail willsuffice. Turn the color control all the way down so you have a B/W picture. Static convergence sets the beams to be coincident in the exact center ofthe screen. This is done using a set of ring magnets behind the puritymagnets on the CRT neck. From the Sams' for the RCA CTC111C: "adjust the center set of magnets toconverge blue to green at the center of the screen. Adjust the rear setof magnets to converge red to green at the center of the screen." Yourset may have a slightly different procedure. Dynamic convergence adjusts for coincidence at the edges and corners. On old tube, hybrid, and early solid state TVs, dynamic convergence wasaccomplished with electronic adjustments of which there may have beena dozen or more that were not independent. With modern sets, all convergenceis done with magnet rings on the neck of the CRT, magnets glued to the CRT,and by tilting the deflection yoke. The clamp in conjunction with rubberwedges or set screws assures that the yoke remains in position. From the Sams' for the RCA CTC111C: "Loosen the screws at the 6 o'clock and10 o'clock positions to permit the yoke to be tilted vertically. Rock yokeup and down to converge the right and left sides of the screen. Tighten screwat 6 o'clock and loosen screw at 3 o'clock to permit the yoke to be tiltedhorizontally. Rock yoke from side to side to converge the top and bottomof the screen. Tighten screws at 3 o'clock and 10 o'clock." Many sets simply use the main clamp which locks the yoke to the neck of theCRT in conjunction with rubber wedges between the yoke and the funnel ofthe CRT to stabilize the yoke position position. Refer to your service manual. (Is this beginning to sound repetitious?) For additional comments on convergence adjustments, see the sections: "Tony'snotes on setting convergence on delta gun CRTs" and "Saga and General setupfor large CRT TVs". Tilted picture:-------------- You have just noticed that the picture on your fancy (or cheap) TVis not quite horizontal - not aligned with the front bezel. Note thatoften there is some keystoning as well where the top and bottom or left andright edges of the picture are not quite parallel - which you may neverhave noticed until now. Since this may not be correctable, adjustingtilt may represent a compromise at best between top/bottom or left/rightalignment of the picture edges. You may never sleep again knowing thatyour TV picture is not perfect! BTW, I can sympathize with your unhappiness.Nothing is more annoying than a just noticeable imperfection such as this.However, since TVs always overscan, the only time you will really notice aminor tilt without going out of your way to look for it is if there is textor graphics near the edge of the screen. There are several possible causes for a tilted picture: 1. Set orientation. The horizontal component of the earth's magnetic field affects this slgithly. Therefore, if you rotate the TV you may be able to correct the tilt. Of course, it will probably want to face the wall! Other external magnetic fields can sometimes cause a rotation without any other obvious effects - have you changed the TV's location? Did an MRI scanner move in next door? 2. Need for degaussing. Most of the time, magnetization of the CRT will result in color problems which will be far more obvious than a slight rotation. However, internal or external shields or other metal parts in the set could become magnetized resulting a tilt. More extensive treatment than provided by the built-in degaussing coil may be needed. Even, the normal manual degaussing procedure may not be enough to get close enough to all the affected parts. 3. You just became aware of it but nothing has changed. Don't dismiss this offhand. It is amazing how much we ignore unless it is brought to our attention. Are you a perfectionist? 4. There is an external tilt control which may be misadjusted. Newer Sony monitors have this (don't know about TVs) - a most wonderful addition. Too bad about the stabilizing wires on Trinitron CRTs. A digital control may have lost its memory accidentally. The circuitry could have a problem. 5. There is an internal tilt control that is misadjusted or not functioning. The existance of such a control is becoming more common. 6. The deflection yoke on the CRT has gotten rotated or was not oriented correctly at the time of the set's manufacture. Sometimes, the entire yoke is glued in place in addition to being clamped adding another complication. If the TV was recently bumped or handled roughly, the yoke may have been knocked out of position. But in most cases, the amount of abuse required to do this with the yoke firmly clamped and/or glued would have totally destroyed the set in the process. There is a risk (in addition to the risk of frying yourself on the various voltages present inside as operating TV) of messing up the convergence or purity when fiddling with the yoke or anything around it since the yoke position on the neck of the tube and its tilt may affect purity and convergence. Tape any rubber wedges under the yoke securely in place as these will maintain the proper position and tilt of the yoke while you are messing with it. (Don't assume the existing tape will hold - the adhesive is probably dry and brittle). 7. The CRT may have rotated slightly with respect to the front bezel. Irrespective of the cause of the tilt, sometimes it is possible to loosen the 4 (typical) CRT mounting screws and correct the tilt by slightly rotating the CRT. This may be easier than rotating the yoke. Just make sure to take proper safety precautions when reaching inside! B/W TV size, position, and geometry adjustments:----------------------------------------------- These tend to be a lot simpler and less critical than for color monitorsor TV sets. On a B/W TV you will probably see some of the following adjustments: 1. Position - a pair of rings with tabs on the neck of the CRT. There may be electronic position adjustements as well though this is not that common on small TVs. 2. Width and height (possibly linearity as well) controls. There may be some interaction between size and linearity - a crosshatch test pattern is best for this. Vertical adjustments are almost always pots while horizontal (if they exist) may be pots and/or coils. Size will normally be set for 5-10% overscan to account for line voltage fluctuations and component drift. Confirm aspect ratio with test pattern which includes square boxes. 3. Geometry - some little magnets either on swivels around the yoke or glued to the CRT. If these shifted, the the edges may have gotten messed up - wiggles, dips, concave or convex shapes. There may be a doxen or more each mostly affecting a region around the edge of the raster. However, they will not be totally independent. Check at extremes of brightness/contrast as there may be some slightchanges in size and position due to imperfect HV regulation. There may be others as well but without a service manual, there is noway of knowing for sure. Sams' often has folders for B/W TVs. Just mark everything carefully before changing - then you will be able toget back where you started. ****************** Low Voltage Power Supply Problems ****************** Low voltage power supply fundamentals:------------------------------------- TVs require a variety of voltages (at various power levels) to function.The function of the low voltage power supply is to take the AC line inputof either 115 VAC 60 Hz (220 VAC 50 Hz or other AC power in Europe andelsewhere) and produce some of these DC voltages. In all cases, the powerto the horizontal output transistor of the horizontal deflection systemis obtained directly from the low voltage power supply. In some cases,a variety of other DC voltages are derived directly from the AC line byrectification, filtering, and regulation. In other designs, however, mostof the low voltages are derived from secondary windings on the flyback(LOPT) transformer of the horizontal deflection system. In still otherdesigns, there is a separate switchmode power supply that provides some orall of these voltages. There are also various (and sometimes convoluted)combinations of any or all of the above. There will always be: 1. A power switch, relay, or triac to enable main power. 2. A set of rectifiers - usually in a bridge configuration - to turn the AC into DC. Small ceramic capacitors are normally placed across the diodes to reduce RF interference. 3. One or more large filter capacitors to smooth the unregulated DC. In the U.S., this is most often a voltage around 150-160 V DC. In countries with 220 VAC power, it will typically be around 300-320 V DC. 4. A discrete, hybrid, or IC regulator to provide stable DC to the horizontal deflection system. Sometimes feedback from a secondary output of the flyback or even the high voltage is used. This regulator may be either a linear or switching type. In some cases, there is no regulator. 5. Zero or more voltage dividers and/or regulators to produce additional voltages directly from the line power. This relatively rare except for startup circuits. These voltages will not be isolated from the line. 6. A degauss control circuit usually including a thermistor or Posistor (a combination of a heater disk and Positive Temperature Coefficient (PTC) thermistor in a single package). When power is turned on, a relatively high AC current is applied to the degauss coil wrapped around the periphery of the CRT. The PTC thermister heats up, increases in resistance, and smoothly decreases the current to nearly zero over a couple of seconds. 7. A startup circuit for booting the horizontal deflection if various voltages to run the TV are derived from the flyback. This may be an IC or discrete multivibrator or something else running off a non-isolated voltage or the standby power supply. 8. A standby power supply for the microcontroller and remote sensor. Usually, this is a separate low voltage power supply using a small power transformer for line isolation. Always use an isolation transformer when working on a TV but this isespecially important - for your safety - when dealing with the non-isolatedline operated power supply. Read and follow the information in the section:"Safety guidelines". Typical TV power supply front end:--------------------------------- The partial schematic below is similar to those found in the majority ofTVs sold in countries with 110 to 120 VAC power. Many parts are not shownincluding the power switch or relay, RFI bypass capacitors across therectifier diodes, and RFI line filter. Bypass resistor Line fuse Main bridge Fusable +----/\/\-----+ _ rectifier resistor +-----+ H o--_ --+------>---+---/\/\--+---+--- REG ---+---+---o B+ +-----+ +--->---+ C1 __ Main __ Regulator 115 VAC 400 uF --- filter --- output +----- N o---------+--- G - Power line earth ground via building wiring * The line fuse is typically 2 to 4 A, usually a normal fast blow type. Even so, it may not blow as a result of faults down the line - the fusable resistor or regulator may fail first. * The main bridge rectifier is often composed of 4 discrete diodes (similar to 1N400Xs) but may also be a single unit. Failures - usually shorted diodes - are common. * The main filter capacitor can range in size from 200 to 800 uF or more at 200 to 250 V. THIS CAN BE LETHAL! A typical TV may continue to work at normal line voltage without any noticeable degradation in performance (hum bars, hum in sound, or shutdown) even if this capacitor is reduced in value by 75%. Its uF value is therefore not critical. * The regulator is often an IC or hybrid module. Failures resulting in no or reduced output, or no regulation are common. * The regulator output capacitor is needed for the B+ regulator to function properly. If this capacitor is reduced in value or develops a high ESR, regulation may fail resulting in instability, oscillation, or excessive B+ and shutdown. * The regulator bypass resistor reduces the amount of current control needed of the regulator. Caution: even if the regulator has been pulled, the B+ line will have substantial voltage as a result of this resistor. Totally dead set:---------------- This can be as simple as a bad outlet (including blown fuse or tripped circuitbreaker due to some other fault), switched outlet and the switch is off, orbad cordset. * Plug a lamp into the outlet to make sure it is live. If the lamp works, then the problem is the TV. It not, the outlet is defective or the fuse is blown or the circuit breaker is tripped. There is another very simple explanation that is sometimes overlooked: This is a switched outlet. You always wondered what that wall switch was for that didn't seem to do anything and you flipped randomly :-). Well, now you know! * Try wiggling the TV's cord both at the outlet (also push the wire toward the plug) and TV (also push the cord toward the TV) with the set on and/or while pressing the power-on button. If you can get a response, even momentarily, the cord likely has broken wires internally. Beyond these basic causes, troubleshooting will be needed inside the set todetermine what is defective. Also see the section: "Intermittently deadset - bad cordset". Intermittently dead set - bad cordset:------------------------------------- There are two problems which are common with the line cord on appliances.Don't overlook these really simple things when troubleshooting your vacuumcleaner - or fancy electronic equipment! If wiggling the cord has an effect,then the following are likely causes: * Repeated flexing results in the internal conductors breaking either at the plug or appliance end. If flexing the cord/squeezing/pulling results in the device going on and off, it is bad. If the problem is at the plug end, cut off the old plug a couple of inches beyond the problem area and replace just he plug. If the problem is at the appliance end, an entire new cordset is best though you can probably cut out the bad section and solder what remains directly to the mainboard. In either case, observe the polarity of the cord wires - they will be marked in some way with a ridge or stripe. It is important that the new plug be of the same type (polarized usually) and that the cord is wired the same way. * The prongs do not fit snugly into older worn outlets. This can usually be remedied by using a pointed tool like an awl or utility knife to spread apart the pair of leaves often used to form each prong of the plug. If the prongs are made of solid metal, it may be possible to spread them apart - widen the space between them. Alternatively, get a 3 to 2 prong adapter just to use as an intermediate connector. Spread the leaves of its prongs. However, a new outlet is best. * Bad connections on the mainboard. As you flex the cord, it is also stressing the attachment to the mainboard and affecting some marginal solder joints. It is important to deal with these symptoms as soon as possible as erraticpower cycling can lead to much more serious and expensive problems down theroad. Power button on set is flakey:----------------------------- If the on/off (or other button) on the set itself behaves erraticallybut the remote control works fine, then it could be a dirty button orcable or other connections to the switch PCB, particularly if the buttonson the set itself are rarely used. There could possibly be a bad pullupresistor or something of that sort - but is it worth the effort to locate? Why not just continue to use the remote? There is no reason to suspect thatit will develop similar symptoms. However, there is some risk that ifthe button is dirty, you may find the TV coming on at random times in themiddle of the night (of course!). I think I have an older Sylvania that does that sort of thing - don'treally know as I never use the power button on the set! If power is controlled by a hard switch - a pull or click knob, or mechanicalpush-push switch and this has become erratic due to worn contacts,replacements are available but often only directly from the originalmanufacturer to physically fit and (where applicable) have the volumeor other controls built in. As an alternative, consider mounting a smalltoggle switch on the side of the cabinet to substitute for the broken switch.This will almost certainly be easier and cheaper - and quite possibly, morereliable. TV blows fuse:------------- If the fuse really blows absolutely instantly with no indication that thecircuits are functioning (no high pitched horizontal deflection whine (ifyour dog hides under the couch whenever the TV is turned on, deflectionis probably working)), then this points to a short somewhere quite nearthe AC power input. The most common places would be: * Degauss Posistor - very likely.* Horizontal output transistor.* Power supply regulator if there is one.* Power supply chopper (switchmode) transistor if there is one.* Diode(s) in main bridge* Main filter capacitor(s). You should be able to eliminate these one by one. Unplug the degauss coil as this will show up as a low resistance. First, measure across the input to the main power rectifiers - itshould not be that low. A reading of only a few ohms may mean ashorted rectifier or two or a shorted Posistor. * Test the rectifiers individually or remove and retest the resistance. * Some sets use a Posistor for degauss control. This is a little cubical (about 1/2" x 3/4" x 1") component with 3 legs. It includes a line operated heater disk (which often shorts out) and a PTC thermister to control current to the degauss coil. Remove the posistor and try power. If the monitor now works, obtain a replacement but in the meantime you just won't have the automatic degauss. If these test good, use an ohmmeter with the set unplugged to measurethe horizontal output transistor. Even better to remove it and measure it. * C-E should be high in at least one direction.* B-E may be high or around 50 ohms but should not be near 0. If any readings are under 5 ohms, the transistor is bad. The partssources listed at the end of this document will have suitable replacements. If the HOT tests bad, try powering the set first with your light bulb and ifit just flashes once when the capacitor is charging, then put a fuse inand try it. The fuse should not blow with the transistor removed. Of course, not much else will work either. If it tests good, power the set without the transistor and see what happens.If the fuse does not blow, then with the good transistor (assuming it is notfailing under load), it would mean that there is some problem with thedriving circuits possibly or with the feedback from the voltages derivedfrom the horizontal not regulating properly. Look inside the TV and see if you can locate any other large power transistorsin metal (TO3) cans or plastic (TOP3) cases. There may be a separatetransistor that does the low voltage regulation or a separate regulatorIC. Some TVs have a switchmode power supply that runs off a differenttransistor than the HOT. There is a chance that one of these may be bad.If it is a simple transistor, the same ohmmeter check should be performed. If none of this proves fruitful, it may be time to try to locate a schematic. A blown fuse is a very common type of fault due to poor design very oftentriggered by power surges due to outages or lightning storms. However,the most likely parts to short are easily tested, usually in-circuit, withan ohmmeter and then easily removed to confirm. If you find the problem and repair it yourself, the cost is likely tobe under $25. Fuse blows or TV blows up when sync is disrupted:------------------------------------------------ This is a problem which is not going to be easy to identify. One possibilityis a drive problem. The messed up sync resulting from swtiching channels,or changing input connections might be resulting in an excessively long scantime for just one scan line. However, this may be enough to cause a currentspike in the horizontal output circuit or an excessive voltage spike on thecollector of the horizontal output transistor. Normally, the HOT currentramps up during scan. During flyback, the current is turned off. Thiscurrent is normally limited and the voltage spike on the collector of theHOT is also limited by the snubber capacitors to a safe value. If scan timeis too long, current continues to increase. At some point, the flyback coresaturates and current goes way up. In addition, the voltage spike will bemuch higher - perhaps destructively so. Troubleshooting these sorts of problems is going to be tough. However,a likely area to investigate would be: * Drive circuitry for the HOT including the coupling components. * The chip that generates takes the sync input and generates the horizontal drive signal. * A bad low voltage regulator might permit the B+ to rise to excessive levels during black scenes (i.e., video mute during channel changing). Internal fuse blew during lightning storm (or elephant hit power pole):---------------------------------------------------------------------- Power surges or nearby lightning strikes can destroy electronic equipment.However, most of the time, damage is minimal or at least easily repaired.With a direct hit, you may not recognize what is left of it! Ideally, electronic equipment should be unplugged (both AC line and phoneline!) during electrical storms if possible. Modern TVs, VCRs, microwaveovens, and even stereo equipment is particularly susceptible to lightning andsurge damage because some parts of the circuitry are always alive and thereforehave a connection to the AC line. Telephones, modems, and faxes are directlyconnected to the phone lines. Better designs include filtering and surgesuppression components built in. With a near-miss, the only thing that mayhappen is for the internal fuse to blow or for the microcontroller to gobonkers and just require power cycling. There is no possible protectionagainst a direct strike. However, devices with power switches that totallybreak the line connection are more robust since it takes much more voltageto jump the gap in the switch than to fry electronic parts. Monitors andTVs may also have their CRTs magnetized due to the electromagnetic fieldsassociated with a lightning strike - similar but on a smaller scale tothe EMP of a nuclear detonation. Was the TV operating or on standby at the time? If it was switchedoff using an actual power switch (not a logic pushbutton or the remotecontrol), then either a component in front of the switch has blown, thesurge was enough to jump the gap between the switch contacts, or it wasjust a coincidence (yeh, right). If the TV was operating or on standby or has no actual power switch, thena number of parts could be fried. TVs usually have their own internal surge protection devices like MOVs (MetalOxide Varistors) after the fuse. So it is possible that all that is wrong isthat the line fuse has blown. Remove the cover (unplug it first!) and startat the line cord. If you find a blown fuse, remove it and measure acrossthe in-board side of fuse holder and the other (should be the neutral) sideof the line. The ohmmeter reading should be fairly high - well certainly notless than 100 ohms - in at least one direction. You may need to unplug thedegaussing coil to get a reasonable reading as its resistance may be 25 or 30ohms. If the reading is really low, there are other problems. If theresistance checks out, replace the fuse and try powering the TV. There willbe 3 possibilities: 1. It will work fine, problem solved. 2. It will immediately blow the fuse. This means there is at least one component shorted - possibilities include an MOV, line rectifiers, main filter cap, regulator transistor, horizontal output transistor, etc. You will need to check with your ohmmeter for shorted semiconductors. Remove any that are suspect and see of the fuse now survives (use the series light bulb to cut your losses - see the section: "The series light bulb trick". 3. It will not work properly or appear dead. This could mean there are open fusable resistors other defective parts in the power supply or elsewhere. In this case further testing will be required and at some point you may need the schematic. If the reading is very low or the fuse blows again, see the section:"TV blows fuse". Fuse replaced but TV clicks with power-on but no other action:------------------------------------------------------------- The click probably means that the power relay is working, though there couldbe bad contacts. Since the fuse doesn't blow now (you did replace it with one of the sameratings, right?), you need to check for: * Other blown fuses - occasionally there are more than one in a TV. Replace with one of exactly the same ratings. * Open fusable resistors. These sometimes blow at the same time or in place of the fuses. They are usually low values like 2 ohms and are in big rectangular ceramic power resistor cases or smaller blue or gray colored cylindrical power resistors. They are supposed to protect expensive parts like the HOT but often blow at the same time. If any of these are bad, they will need to be replaced with flameproofresistors of the same ratings (though you can substitute an ordinaryresistor for testing purposes). Before applying power, check: Rectifierdiodes, horizontal output transistor, regulator pass or chopper transistor(if present), and main filter capacitor for shorts. An initial test with an ohmmeter can be done while in-circuit. Theresistance across each diode and the collector to emitter of thetransistors should be relatively high - a few hundred ohms at lest -in at least one direction (in-circuit). If there is a question, unsolderone side of each diode and check - should be in the Megohms or higher inone direction. Removed from the circuit, the collector-emitter resistanceshould be very high in one direction at least. Depending on the type,the base-emitter resistance may be high in one direction or around 50 ohms.If any reading on a semiconductor device is under 10 ohms - then the devicemost likely bad. Assuming that you do not have a schematic, you shouldbe able to locate the rectifiers near where the line cord is connected andtrace the circuit. The transistors will be either in a TO3 large metal canor a TOP3 plastic package - on heat sinks. The filter capacitor shouldeventually measure high in one direction (it will take a while to chargefrom your ohmmeter). It could still be failing at full voltage, however. If you find one bad part, still check everything else as more than one partmay fail and just replacing one may cause it to fail again. Assuming everything here checks out, clip a voltmeter set on its 500 V scaleor higher across the horizontal output transistor and turn the power on.Warning - never measure this point if the horizontal deflection is operating.it is ok now since the set is dead. If the voltage here is 100-150, thenthere is a problem in the drive to the horizontal output circuit. If itis low or 0, then there are still problems in the power supply or with thewinding on the flyback transformer. Other possible problems: bad hybrid voltage regulator, bad startup circuit,bad standby power supply (dried up filter capacitor, etc.) bad relay contactsas mentioned above. However, these probably would not have blown the fuse inthe first place so are less likely. Power-on tick-tick-tick or click-click-click but no other action:---------------------------------------------------------------- A variety of power supply or startup problems can result in this orsimilar behavior. Possibilities include: * Lack of startup horizontal drive - see the section: "Startup problems - nothing happens, click, or tick-tick-tick sound". The main regulator is cycling on overvoltage due to lack of load. * Excessive load or faulty power supply cycling on its overcurrent protection circuit. * High voltage shutdown, or some other system detecting an out of regulation condition. However, in this case, there should be some indication that the deflection and HV is attempting to come up - momentary whine, static on the screen, etc. * A dried up main filter capacitor or other filter capacitor in the low voltage power supply that is producing an out-of-regulation condition until it warms up. A bad filter capacitor on the output of a series regulator may result in excessive voltage and subsequent shutdown. * A problem with the microcontroller, relay or its driver, or standby power supply. One possible test would be to vary the line voltage and observe theset's behavior. It may work fine at one extreme (usually low) or theother. This might give clues as to what is wrong. Also see the section: "Dead TV with periodic tweet-tweet, flub-flub, orlow-low voltage". No picture or raster and no sound:--------------------------------- The screen is blank with no raster at all. There are indications that thechannel numbers are changing in the display. This indicates that some of thelow voltages are present but these may be derived from the standby supply. Assuming there is no deflection and no HV, you either have a low voltage powersupply problem, bad startup circuit, or bad horizontal output transistor(HOT) or other bad parts in the horizontal deflection. Check for bad fuses. (If you have HV as indicated by static electricity on the front of thescreen and you hear the high pitched whine of the horizontal deflectionwhen it is turned on, then the following does not apply). 1. Use an ohmmeter to test the HOT for shorts. If it is bad, look for open fusable resistors or other fuses you did not catch. 2. Assuming it is good, measure the voltage on the collector-emitter of the HOT (this is safe if there is no deflection). You should see the B+ - probably between 100 and 150 V. 3. If there is no voltage, you have a low voltage power supply problem and/or you have not found all the bad/open parts. 4. If there is voltage and no deflection (no high pitched whine and no HV), you probably have a startup problem - all TVs need some kind of circuit to kick start the horizontal deflection until the auxiliary power outputs of the flyback are available. Some Zeniths use a simple multivibrator for this - a couple of transistors. Others power the horizontal osc. IC from a special line-derived voltage. The multivibrator type are sometimes designed to fail if someone keeps turning the set on and off (like kids playing) since the power rating is inadequate. Test the transistors if it is that type with an ohmmeter. If one is shorted, you have a problem. The usual way a TV service person would test for startup problems is to inject a signal to the base of the HOT of about 15.75 KHz. If the TV then starts and runs once this signal is removed, the diagnosis is confirmed. This is risky - you can blow things up if not careful (including yourself). If you hear the high pitched whine of the deflection and/or feel some staticon the scree, confirm that the horizontal deflection and high voltage areworking by adjusting the SCREEN control (probably on the flyback). If you canget a raster then your problem is probably in the video or chromacircuits, not the deflection or high voltage. Reduced width picture and/or hum bars in picture and/or hum in sound:-------------------------------------------------------------------- The most likely cause is a dried up main filter capacitor. Once theeffective capacitance drops low enough, 120 Hz (or 100 Hz in countries with50 Hz power) ripple will make its way into the regulated DC supply(assuming full wave rectification). Another likely cause of similar symptoms is a defective low voltageregulator allowing excessive ripple. The regulator IC could be bador filter capacitor following the IC could be dried up. Either of these faults may cause: 1. A pair of wiggles and/or hum bars in the picture which will float up the screen. For NTSC where the power line is 60 Hz but the frame rate is 59.94 Hz, it will take about 8 seconds for each bar to pass a given point on the screen. (On some sets, a half wave recitifier is used resulting in a single wiggle or hum bar). 2. Hum in the sound. This may or may not be noticeable with the volume turned down. 3. Possible regulation problems resulting in HV or total shutdown or power cycling on and off. The best approach to testing the capacitors is to clip a good capacitor ofapproximately the same uF rating and at least the same voltage rating acrossthe suspect capacitor (with the power off). A capacitor meter can alsobe used but the capacitor may need to be removed from the circuit. Once the capacitors have been confirmed to be good, voltage measurementson the regulator should be able to narrow down the problem to a bad ICor other component. Excessive B+ from fixed regulator like STR30123/STR30130/STR30135:----------------------------------------------------------------- These are fixed regulators that do fail but the problem may be elsewhere. If the B+ goes to high, the X-ray protection circuitry may kick in and shutdown the horizontal deflection. If there is little or no load (horizontal deflection not running at all), allbets are off as well - the resistor that is likely across input-output willdominate and boost the voltage above the proper output for the regulatorchip. Use a Variac to bring up the voltage to the TV. If the deflectiondoes not start up at any voltage even with the B+ ramping up past its normalvalue, the problem is probably in the horizontal deflection/startup circuitry,not the regulator. Some of these may go out of regulation if the output electrolytics are driedup. There might a a 10 uF 200 V or so electrolytic across the output toground. Test it or substitute a known good one of about the same uF ratingand at least equal voltage rating. If you can get the TV to work at reducedvoltage using a Variac (but possibly with hum bars in the picture and hum inthe audio), check the output capacitor. Otherwise, it could be the regulator or one of its biasing components (setscurrent to B input - the voltage at this input should be close to theoutput voltage value). Also check to be sure the input voltage is solid -main filter capacitor is not dried up. TV power cycling on and off:--------------------------- The power light may be flashing or if you are runing with a serieslight bulb it may be cycling on and off continuously. There may bea chirping or clicking sound from inside the set. (Note: using too small aseries light bulb load during testing for the size of the TV may also resultin this condition.) If there is a low voltage regulator or separate switching supply, itcould be cycling on and off if the horizontal output, flyback, orone of its secondary loads were defective. Does this TV have a separate low voltage regulator and/or switching powersupply or is it all part of the flyback circuit? For the following, I assumeit is all in one (most common). Some simple things to try first: Verify that the main filter capacitor is doing its job. Excessive rippleon the rectified line voltage bus can cause various forms of shutdownbehavior. An easy test is to jumper across the capacitor with one ofat least equal voltage rating and similar capacitance (make connectionswith power off!). Use a Variac, if possible, to bring up the input voltage slowly and see ifthe TV works at any point without shutting down. If it does, this could bean indication of X-ray protection circuit kicking in, though this willusually latch and keep the set shut off if excessive HV were detected. Dead TV with periodic tweet-tweet, flub-flub, or low-low voltage:---------------------------------------------------------------- A TV which appears to be dead except for a once a second or so tweet or flubusually indicates an overload fault in the power supply or a short in one ofits load circuits. In some cases, the low voltage (including B+) will just bereduced to a fraction of their normal value as a result of an overload on oneof the outputs - usually the main B+. This may be caused by a shorted rectifier in the power supply, flyback, oreven the yoke, but check the the loads first. Wait a few minutes for thefilter caps to discharge (but stay away from the CRT HV connector as it mayretain a dangerous and painful charge for a long time), use an ohmmeter acrossthe various diodes in the power supply. Using an ohmmeter on the rectifierdiodes, the resistance in at least one direction should be greater than 100ohms. If it is much less (like 0 or 5 ohms), then the diode is probably bad.Unsolder and check again - it should test infinite (greater than 1M ohms) inone direction. Summary of possible causes: * Bad solder connections. * Other shorted components like capacitors. * Other problems in the power supply or its controller. * Bad flyback. * Short or excessive load on secondary supplies fed from flyback. * Short in horizontal yoke windings. * Problem with startup drive (cycling on overvoltage). Shorted Components:------------------ A failure of the horizontal output transistor or power supply switchmodetransistor will blow a fuse or fusable resistor. Look for blown fuses and test for open fusable resistors in the power circuits.If you find one, then test the HOT and/or switchmode transistor for shorts. Other possibilities: rectifier diodes or main filter capacitor. While you are at it, check for bad connections - prod the circuit board with aninsulated stick when the problem reoccurs - as these can cause parts tofail. Startup problems - nothing happens, click, or tick-tick-tick sound:------------------------------------------------------------------ TVs and monitors usually incorporate some kind of startup circuit to providedrive to the horizontal output transistor (HOT) until the flyback power supplyis running. Yes, TVs and monitors boot just like computers. There are two typical kinds of symptoms: power on click but nothing elsehappens or a tick-tick-tick sound indicating cycling of the low voltage(line regulator) but lack of startup horizontal drive. Check the voltage on the horizontal output transistor (HOT). If no voltageis present, there may be a blown fuse or open fusable resistor - andprobably a shorted HOT. However, if the voltage is normal (or high) - usually 100-150 V, thenthere is likely a problem with the startup circuit not providing initialbase drive to the HOT. The startup circuits may take several forms: 1. Discrete multivibrator or other simple transistor circuit to provide base drive to the HOT. 2. IC which is part of deflection chain powered off of a voltage divider or transformer. 3. Other type of circuit which operates off of the line which provides some kind of drive to the HOT. The startup circuit may operate off of the standby power supply orvoltage derived from non-isolated input. Be careful - of course, usean isolation transformer whenever working on TVs and especially for powersupply problems. Note that one common way of verifying that this is a startup problem isto inject a 15 KHz signal directly into the HOT base or driver circuit(just for a second or two). If the TV then starts up and continues to run,you know that it is a startup problem. Caution: be careful if you do this. The HOT circuit may be line-connectedand it is possible to destroy the HOT and related components if this is notdone properly. I once managed to kill not only the HOT but the choppertransistor as well while working in this area. An expensive lesson. I have also seen startup circuits that were designed to fail. Turningthe TV on and off multiple times would exceed the power ratings of thecomponents in the startup circuit. Some Zenith models have this 'feature'. When this situation exists, it could be that the circuit is not providingthe proper drive or that due to some other circuit condition, the driveis not always sufficient to get the secondary supplies going to the pointthat the normal circuits take over. I would still check for bad connections - prod the circuit board with aninsulated stick when the problem reoccurs. TV turns off after warming up:----------------------------- If you can turn it back on with the s momentary key or power button: When it shuts off, do you need to push the power button once or twiceto get it back on? Also, does anything else about the picture or soundchange as it warms up? 1. If once, then the controller is shutting the TV down either as a result of a (thermally induced) fault in the controller or it sensing some other problem. Monitoring the voltage on the relay coil (assuming these is one) could help determine what is happening. The controller thinks it is in charge. 2. If twice, then the power supply is shutting down as the controller still thinks it is on and you are resetting it. A couple of possibilities here would be low voltage or high voltage regulation error (excessive high voltage is sensed and causes shutdown to prevent dangerous X-ray emission). A partially dried up main filter capacitor could also cause a shutdown but there might be other symptoms like hum bars in the picture just before this happened. Clipping a good capacitor across the suspect (with power off!) would confirm or eliminate this possibility. If it uses a pull-knob (or other hard on/off switch), then this may be likepulling the plug and would reset any abnormal condition. TV doesn't power up immediately:------------------------------- The TV may do nothing, cycle on and off for a while, power up and thenshutdown in an endless cycle - or at least for a while. Then it comeson and operates normally until it is turned off. A couple of possibilities: 1. The main filter capacitor or other filter capacitors in the low voltage power supply is dried up and this can cause all kinds of regulation problems. 2. The power supply regulator is defective (or marginal) allowing excessive voltage on its output and then the X-ray protection circuitry shuts you down. If you can get access to a Variac, it would be worth bringing up the inputvoltage slowly and seeing if there is some point at which it would stay on. If there is, then if the picture has serious hum bars in it the main filtercap could be bad. If more or less a decent picture with minor hum bars thenit could be the regulator. Old TV requires warmup period:----------------------------- So, what else is new? In the old days, a TV was expected to take a fewminutes (at least) to warm up. We are all spoiled today. Of course, youusually maintained a full time technician or engineer to fiddle with theconvergence adjustments! A TV (from around 1983) needs at least 5 min. to warm up (lighting up thescreen and making sound if I give it a cold start. Once warmed up, youcan it off and on again from the front panel and it will work immediately.Another thing this TV has a sub-power switch in the rear. 1983 sounds a bit late, but sets in the late '70 during the transition fromtubes to all solid state chassis often had the 'sub-power' switch providingsome power to the filaments of the CRT and other tubes - usually in thedeflection and high voltage circuits since these would take a while to heat upand stabilize. The idea was to leave this switch on all the time (except whengoing on vacation - it was sometimes labeled 'vacation') so that you wouldhave nearly instant warm up. Supposedly, this led to an increased risk offire as well (see the section: "About instant-on TVs"). If it is a totally solid state chassis, then there is some component - probablya capacitor in the power supply since it affects both picture and sound - thatis drifting with temperature and needs to be located with cold spray or aheat gun. TV shuts down with bright picture or when brightness is turned up:----------------------------------------------------------------- This is probably a protection circuit kicking in especially if turning poweroff or pulling the plug is required to restore operation. The detection circuit could be in the power supply or horizontal deflectionoutput circuit. It may be defective or the current may be too high for someother reason. A couple of tests can be performed to confirm that it is dueto beam current: * Determine if behavior is similar when adjusting the user brightness control and the screen (G2) pot (on the flyback) or master brightness control. If the TV quits at about the same brightness level, overcurrent protection is likely. * Disconnect the filaments to the CRT (unsolder a pin on the CRT socket) and see if it still shuts down under the same conditions. If it is overcurrent protection, shut down should now *not* take place since there is no beam current. Relays in the Power Circuitry of TVs:------------------------------------ What exactly is the purpose of such a relay ... i.e., why doesn't thepower switch on the TV just apply power directly instead of through arelay? The usual reason for a relay instead of a knob switch is to permit a remotecontrol to turn power on and off. If your TV does not have a remote, thenit is simply the same chassis minus 24 cents worth of circuitry to do theremote function. Isn't marketing wonderful? The only unknown is the coil voltage. It is probably somewhere inthe 6-12 volt range. You should be able to measure this on the coilterminals in operation. It will be a DC coil. However, the relay controls the 125 VAC (or 220) which you should treatwith respect - it is a lot more dangerous than the 25KV+ on the CRT! Almost certainly, the relay will have 4 connections - 2 for power and 2for the coil. If it is not marked then, it should be pretty easy tolocate the power connection. One end will go to stuff near the AC lineand the other end will go to the rectifier or maybe a fusable resistoror something like that. These will likely be beefier than the coilconnections which will go between a transistor and GND or some low voltage,or maybe directly into a big microcontroller chip. Of course, the best thing would be to get the schematic. Some big publiclibraries carry the Sams' photofact series for TVs and VCRs. If not, take10 minutes and trace it. You should be able to get far enough to determinethe relay connections. Once you are sure of the AC connections - measure across them while it isoff and also while it is on. While off, you should get 110-125 VAC.While on and working - 0. While on and not working either 110-125 VACif the relay is not pulling in or 0 if it is and the problem is elsewhere.We can deal with the latter case if needed later on. Note the even if therelay contacts are not working, the problem could still be in the controlcircuitry not providing the correct coil voltage/current, though not likely. It may be expensive and/or difficult to obtain an exact replacement, butthese are pretty vanilla flavored as relays go. Any good electronicsdistributor should be able to supply a suitable electrical replacementthough you may need to be creative in mounting it. Flameproof Resistors:-------------------- Flameproof Resistor or Fusable Resistor are often designated by thesymbol 'FR'. They are the same. You may see these in the switchmode power supplies used in TVs and monitors.They will look like power resistors but will be colored blue or gray, or maybe rectangular ceramic blocks. They should only be replaced with flameproofresistors with identical ratings. They serve a very important safety function. These usually serve as fuses in addition to any other fuses that may bepresent (and in addition to their function as a resistor, though this isn'talways needed). Since your FR has blown, you probably have shortedsemiconductors that will need to be replaced as well. I would checkall the transistors and diodes in the power supply with an ohmmeter.You may find that the main switch mode transistor has decided to turn intoa blob of solder - dead short. Check everything out even if you find onebad part - many components can fail or cause other components to failif you don't locate them all. Check resistors as well, even if they look ok. Since they function as fuses, flameproof resistors should not be replacedwith higher wattage types unless specifically allowed by the manufacturer.These would not blow at the same level of overload possibly resulting indamage to other parts of the circuitry and increasing the risk of fire. Then, with a load on the output of the power supply use a Variac to bringup the voltage slowly and observe what happens. At 50 VAC or less, theswitcher should kick in and produce some output though correct regulationmay not occur until 80 VAC or more. The outputs voltages may even begreater than spec'd with a small load before regulation is correct. Width and height change with warmup:----------------------------------- Since both width and height are affected, this points to something commonlike the low voltage power supply. If there are any indications of humbars, first check the main filter capacitor(s) or substitute a knowngood one. There might even be other symptoms like faint retrace lineson at least part of the screen. Start by monitoring the B+ to the flyback (feeding the HOT) to see if thisdrifts at all. If it does, then there is probably a low voltage regulatorproblem - bad capacitor, resistor, or chip. Use freeze spray to narrowit down. If this is solid, then there could be a high voltage drift butthis would be somewhat unusual without other symptoms (like arcing) sincethe HV is nearly always tracks the low voltage supply. Problems with SCR based regulators:---------------------------------- "Sharp TV has a short blast of high voltage and sound then shuts down. All components in regulator area test good. I have two of these sets." Is there a good sharp tech out there thats seen this problem?" (From: Mr. Caldwell (jcaldwel@iquest.net)). There is a bulletin from Sharp on troubleshooting *any* SCR regulated TV, thiscan easily be adapted to RCA, GE, Emerson and Panasonic sets that have similar circuits given a little thought but the technician. You are going to need to figure part of this out as I no longer have theschematics available. All this will do is allow you to rule out either theregulator or the horizontal section. Don't plug this in until you've read the whole list. Figure out how to bypass the turn on circuit from the microprocessor (unlessit's a manual one). This is usually just jumpering the relay but sometimesSharp puts a horizontal Vcc turn on transistor that also must be jumpered. Next jumper across the SCR anode to cathode. Now using an *variable isolation transformer* turn the voltage on it down andplug the set in. Bring the voltage up slowly, if you can bring the AC up sothat the DC on the jumper across the SCR is within the regulated voltage youshould have a picture and this rules out the horizontal section as theculprit. If the set shuts down prior to getting the DC up enough then you've got problems in the horizontal section. Either you have something wrong with thehigh voltage transformer or the tuning caps or there is a problem with thex-ray protect pick off voltage to the deflection IC. If it's the horizontal section you can set the AC at approx. 25v and look at the waveforms in the horizontal output section for defects like ringing. I've never gotten a good troubleshooting technique down for the regulatorsince it's an active circuit the waveforms and voltages are not stable when it's failed. A good diode, transistor and capacitor checker will help. It would help to get the service manual for that set, the training manualfor that chassis and the bulletin dealing with troubleshooting SCR regulators. Also the training manual should have a good explanation of how this regulator works. In a nutshell the regulator is a switched mode circuit that uses a winding from the high voltage transformer to turn off the SCR.The regulator is always turned off at the same time by a pulse from the high voltage transformer. Regulation is achieved by controlling when the SCR is allowed to turn on. TV shuts down with dark picture or when changing channels:--------------------------------------------------------- This may happen at any time or possibly after being on for awhile in whichsomething heats up and drifts out of spec. The low voltage regulator may be letting the voltage rise excessively. Then,a dark picture or video muting during a channel change triggers the X-rayor power supply overvoltage protection. Monitor the output of the low voltage power supply B+ to see if it is stableas the brightness/scene changes. ********************* Deflection Problems ********************* Deflection fundamentals:----------------------- Note: the following is just a brief introduction. For more detailed deflectionsystem theory of operationo and sample circuits, see the document: "TV andMonitor Deflection Systems". The electron beams in the CRT need to be scanned horizontally and verticallyin a very precise manner to produce a raster - and a picture. For NTSC and PAL, the horizontal scan rates are 15,734 and 15,625 Hzrespectively. For NTSC and PAL, the vertical scan rates are 60 and 50 Hz (approximately)respectively. The deflection yoke includes sets of coils for horizontal and verticalscanning oriented at 90 degrees with respect to each other. Additionalcoils are needed to correct for pincushion and other geometric defects. The deflection circuits must be synchronized and phase locked to theincoming video signal. Therefore, we have the following functions: 1. Sync separator to obtain horizontal and vertical synchronization pulses. 2. Horizontal oscillator which locks to horizontal sync pulses. 3. Horizontal drive followed by horizontal output which feeds deflection yoke (and flyback for HV and other voltages), Yoke requires a sawtooth current waveform for linear horizontal deflection. Horizontal output in all but the smaller TVs is a large discrete power transistor, most often an NPN bipolar type. 4. Vertical oscillator which locks to vertical sync pulses. Yoke requires sawtooth waveform for linear vertical deflection. 5. Vertical drive/output which feeds vertical deflection yoke. Newer TVs use ICs for vertical drive and output. 6. Various additional deflection signals to correct for the imperfections in the geometry of large angle deflection CRTs. These may be fed into the normal deflection coils and/or there may be separate coils mounted on the neck of the CRT. About the vertical scan rate:---------------------------- Some people believe that the TV scan rate is locked to the local power line.TVs never ever used the line frequency for vertical rate. The vertical rateis not even equal to line frequency, actually 59.94 Hz (NTSC). It was setoriginally to 60 Hz to minimize the visibility of interference between thedeflection and power transformer. When NTSC added color, it changed to59.94 Hz for highly technical reasons. And, TVs no longer have powertransformers. Picture squeezed in then died:----------------------------- You were watching 'Knight Rider' reruns and all of a sudden, the picture"squeezed in" slowly from the right hand side. It "squeezed in" about 2 inches or so when the entire picture went dead - has remained like this since.Sound is fine, but no activity at all from the tube. Has it died? Howmuch time, effort, and expense to fix? No, it's not dead, at least it certainly is not the picture tube. Your set probably didn't like Knight Rider - at least that episode! Seriously, how old is the set? Is it a totally solid state chassis orare there tubes in the deflection circuits? Is there any indication of light on the screen? Any indication of the 15735 Hzhorizontal running at all? (You would normally hear the high pitch sound). Newer TVs almost always derive voltages for the sound circuits from thehorizontal deflection but older hybrids may run the sound off of its ownpower. In any case, there is a problem in the horizontal deflection and you probablyhave no high voltage as well assuming no light on the screen. The fact that it squeezed in first indicates that a partial short or otherfault may have developed in the horizontal deflection circuits - possiblythe deflection yoke or flyback transformer. It could also have been a badconnection letting loose. Once it failed completely, the horizontal outputtransistor may have bought the farm or blown a fuse. Horizontal deflection shutting down:----------------------------------- Confirm that the horizontal deflection is shutting down (along with thehigh voltage since it is derived from horizontal deflection: listenfor the high pitched deflection whine, test for static on the screen,see if the CRT filaments are lit, turn up the brightness and/or screencontrol to see if you can get a raster) and then why: 1) Power is failing to the horizontal output transistor - this could be due to a low voltage power supply problem, bad connection, etc. 2) Base drive to the horizontal output transistor is failing - could be a fault in the horizontal oscillator or bad connection. 3) Problem with the flyback transformer or its secondary loads (flyback may provide other power voltages). 4. X-ray protection is activating - either due to excess HV or due to a fault in the X-ray protection circuitry. If the problem comes and goes erratically it sounds like a bad connection,especially if whacking has an effect. If it comes and goes periodically,then a component could be heating up and failing, then cooling, etc. Horizontal lock lost:-------------------- A TV which loses horizontal lock when changing channels, momentarilylosing the signal, or switching inputs may have a horizontal oscillatorthat is way out of adjustment or has drifted in frequency due to agingcomponents. Note that the characteristics of this are distinctly different thanfor total loss of sync. In the latter case, the picture will drift sidewaysand/or up and down while with an off frequency oscillator, the torn uppicture will try at least to remain stationary. This could be a capacitor or other similar part. Or, the oscillatorfrequency may just need to be tweaked (particularly with older sets).There may be an internal horizontal frequency adjustment - either a potor a coil - which may need a slight tweak. If a coil, use a plasticalignment tool, not metal to avoid cracking the fragile core. A schematic will be useful to locate the adjustment if any or to identifypossible defective parts. Try a large public library for the Sams' Photofactfor this set. Insufficient width (without hum bars):------------------------------------- If there are hum bars or wiggles in the picture and/or hum in the sound, seethe section: "Reduced width picture and/or hum bars in picture and/or hum insound". If both width and height are affected, the cause is likely something common:low, low voltage power supply voltages or excessive high voltage (resultingin a 'stiffer' beam). (From: Jerry G. (jerryg@total.net)). Lack of width is usually caused by defective power supply, low horizontaldrive to the yoke and flyback, defective circuits in the pincushioningamplifier section, excessive high-voltage caused by defective voltageregulation, and or excessive loading on the secondary side of the flyback. Vertical lock lost:------------------- This indicates a picture that is correct but rolling vertically. If the picture is rolling down the screen the frequency of the verticaloscillator is incorrect - too high - and this may be the problem. Generally,the free run frequency of the vertical oscillator should be a little belowthe video rate (of around 50 or 60 Hz depending on where you live). If it is rolling continuously without jumping, then there is a loss ofsync from the sync separator or faulty components in the vertical oscillatorcausing it to totally ignore the sync pulses. If it is rolling up rapidly and not quite able to remain locked, the freerun frequency may be too low or there could be a fault in the sync circuitsresulting in an inadequate vertical pull-in range. On older sets, there was actually a vertical hold (and possibly even aseparate vertical frequency) control. On anything made in the last decade,this is unlikely. There may be Vertical Frequency and Vertical Pull-inRange adjustments (and others) accessible via the service menu. However,if any of these ever change, it indicates a possible problem with the EEPROMlosing its memory as component drift is unlikely. As with everything else, bad connections are possible as well. You will needa schematic and possibly setup info to go beyond this. Vertical squashed:----------------- This is a vertical deflection problem - possibly a bad capacitor, badconnection, flyback/pumpup diode, or other component. None of these shouldbe very expensive (in a relative sort of way). If the symptoms change - particularly if they become less severe - as the setwarms up, a dried up electrolytic capacitor is most likely. If they getworse, it could be a bad semiconductor. Freeze spray or a heat gun may beuseful in identifying the defective component. It is often easiest to substitute a good capacitor for each electrolytic inthe vertical output circuit. Look for bad connections (particularly to thedeflection yoke), then consider replacing the vertical output IC ortransistor(s). A defective deflection yoke is also possible or in rare cases, a bad yokedamping resistor (e.g., 500 ohms, may be mounted on the yoke assembly itself). The following are NOT possible: CRT, flyback, tuner (except for the famousRCA/GE/Proscan or Sony models where the controller is at fault - see thesections on these specific brands). I am just trying to think of reallyexpensive parts that cannot possibly be at fault :-). Note that some movies or laser karaoke discs are recorded in 'letterbox'format which at first glance looks like a squashed vertical problem. However,the picture aspect ratio will be correct and turning up the brightness willreveal a perfectly normal raster above and below the picture. Part of picture cut off:----------------------- The following applies if the part of the picture is missing but nototherwise squashed or distorted. For example, 85% is missing but theportion still visible is normal size. Wow! That's an interesting one, more so than the typical run-of-the-mill"my TV just up and died on me". Or, "my pet orangutan just put a holein the CRT, what should I do"? Since the size of the picture fragment is correct but 85% is missing,my first thought would be to check waveforms going into the verticaloutput stage. The supply voltage is probably correct since that oftendetermines the size. It almost sounds like the waveform rather thanbeing mostly on (active video) and off for the short blanking periodis somehow only on during the last part of the active video thus givingyou just the bottom of the picture. If there is a vertical output IC,it may be defective or the blanking input to it may be corrupted. Theproblem may be as far back as the sync separator. Then again who knows,maybe wait for the schematics. Single Vertical Line:-------------------- CAUTION: To prevent damage to the CRT phosphors, immediately turn down thebrightness so the line is just barely visible. If the user controls do nothave enough range, you will have to locate and adjust the master brightness orscreen/G2 pots. Since you have high voltage, the horizontal deflection circuits are almostcertainly working (unless there is a separate high voltage power supply -almost unheard of in modern TVs and very uncommon in all but the mostexpensive monitors). Check for bad solder connections between the main board and the deflectionyoke. Could also be a bad horizontal coil in the yoke, linearity coil, etc.There is not that much to go bad based on these symptoms assuming the high voltage and the horizontal deflection use the same flyback. It is almostcertainly not an IC or transistor that is bad. Single Horizontal Line:---------------------- CAUTION: To prevent damage to the CRT phosphors, immediately turn down thebrightness so the line is just barely visible. If the user controls do nothave enough range, you will have to locate and adjust the master brightness orscreen/G2 pots. A single horizontal line means that you have lost vertical deflection.High voltage is most likely fine since there is something on the screen. This could be due to: 1. Dirty service switch contacts. There is often a small switch on the located inside on the main board or perhaps accessible from the back. This is used during setup to set the color background levels. (On some sets, this is located on the CRT neck board and may be a jumper plug or other means of selecting service mode - not an actual switch). When moved to the 'service' position, it kills vertical deflection and video to the CRT. If the switch somehow changed position or got dirty or corroded contacts, you will have this symptom. Flip the switch back and forth a couple of times. If there is some change, then replace, clean, resolder, or even bypass it as appropriate. 2. Bad connection to deflection yoke or other parts in vertical output circuit. Bad connections are common in TVs and monitors. Check around the pins of large components like transformers, power transistors and resistors, or connectors for hairline cracks in the solder. Reseat internal connectors. Check particularly around the connector to the deflection yoke on the CRT. 3. Bad vertical deflection IC or transistor. You will probably need the service manual for this and the following. However, if the vertical deflection is done with an IC, the ECG Semiconductor Master Substitution guide may have its pinout which may be enough to test it with a scope. 4. Other bad parts in vertical deflection circuit though there are not that many parts that would kill the deflection entirely. 5. Loss of power to vertical deflection circuits. Check for blown fusable resistors/fuses and bad connections. 6. Loss of vertical oscillator or vertical drive signals. The most likely possibilities are in the deflection output stage orbad connections to the yoke. Keystone shaped picture:----------------------- This means that the size of the picture is not constant from top to bottom(width changes) or left to right (height changes). Note that some slightamount of keystoning is probably just within the manufacturing tolerance ofthe deflection yoke and factory setup (geometry magnet placement, if any). Ona TV, this is only noticeable with scenes having straight edges (e.g., videogames) in relationship to the CRT bezel. However, a sudden increase (and it will usually be rather substantial in aTV) may indicate a problem with the deflection yoke. An open or short in a winding (or any associated components mounted on the yokeassembly) will result in the beam being deflected less strongly on the sidewhere that winding is located. Typical TV yokes have fewer individual windingsin parallel than high scan rate monitors so the effects of one such fault aremore dramatic. See the section: "Deflection yoke testing". If the set has been dropped off a 20 story building, the yoke may have shiftedits position on the neck, of the CRT resulting in all sorts of geometry andconvergence problems (at the very least). Loss of Horizontal Sync (also applies to vertical) after Warmup:--------------------------------------------------------------- The problem lies either in the horizontal oscillator or in the sync system.If it really is a problem with sync pulses not reaching the oscillator,the picture will move around horizontally and can be brought to holdmomentarily with the hold control. If the picture breaks up into strips,there is a problem in the horizontal oscillator. Rotate the hold control:if the frequency is too far off, the picture will not settle into placeat any adjustment of the hold control. Look around the horizontal oscillatorcircuit: all of the oscillator parts will be right there, or check on the horizontal oscillator module. Another horizontal problem can occurif the set is an RCA made from around 1972-1980: these sets are designedto slip very far off sync if the high voltage is too high, to protectagainst radiation. Turning up the brightness will decrease the numberof bars if this system is in question, as the high voltage is decreasing.In this case, check around the high-voltage regulation system on the deflection systems board. I've had 2 1970's RCA's with this problem. Intermittent jumping or jittering of picture or other random behavior:--------------------------------------------------------------------- This has all the classic symptoms of a loose connection internal to theTV or monitor - probably where the deflection yoke plugs into the main PCB orat the base of the flyback transformer. TVs and monitors are notorious forboth poor quality soldering and bad connections near high wattage componentswhich just develop over time from temperature cycling. The following is not very scientific, but it works: Have you tried whackingthe TV when this happened and did it have any effect? If yes, this wouldbe further confirmation of loose connections. What you need to do is examine the solder connections on the PCBs in themonitor, particularly in the area of the deflection circuits and power supply.Look for hairline cracks between the solder and the component pins - mostlythe fat pins of transformers, connectors, and high wattage resistors. Anythat are found will need to be reflowed with a medium wattage (like 40W) ortemperature controlled soldering iron. It could also be a component momentarily breaking down in the power supplyor deflection circuits. One other possibility is that there is arcing or corona as a result of humidweather. This could trigger the power supply to shut down perhapswith a squeak, but there would probably be additional symptoms includingpossibly partial loss of brightness or focus before it shut down. You mayalso hear a sizzling sound accompanied by noise or snow in the picture,static in the sounds, and/or a smell of ozone. Horizontal output transistors keep blowing (or excessively hot):--------------------------------------------------------------- Unfortunately, these sorts of problems are often difficult to definitivelydiagnose and repair and will often involve expensive component swapping. You have just replaced an obviously blown (shorted) horizontal outputtransistor (HOT) and an hour (or a minute) later the same symptomsappear. Or, you notice that the new HOT is hotter than expected: Would the next logical step be a new flyback (LOPT)? Not necessarily. If the set performed normally until it died, there are other possiblecauses. However, it could be the flyback failing under load or when itwarms up. I would expect some warning though - like the picture shrinksfor a few seconds before the poof. Other possible causes: 1. Improper drive to horizontal output transistor (HOT). A weak drive might cause the HOT to turn on or (more likely) shut off too slowly (greatly increasing heat dissipation. Check driver and HOT base circuit components. Dried up capacitors, open resistors or chokes, bad connections, or a driver transformer with shorted windings or broken or loose core can all affect drive waveforms. 2. Excessive voltage on HOT collector - check LV regulator (and line voltage if this is a field repair), if any. 3. Defective safety capacitors or damper diode around HOT. (Though this usually results in instant destruction with little heating). 4. New transistor not mounted properly to heat sink - probably needs mica washer and heat sink compound. 5. Replacement transistor not correct or inferior cross reference. Sometimes, the horizontal deflection is designed based on the quirks of a particular transistor. Substitutes may not work reliably. 6. CRT shorting internally. If this happens only once in two weeks, it may be diffuclt to track down :-(. The HOT should not run hot if properly mounted to the heat sink (usingheatsink compound). It should not be too hot to touch (CAREFUL - don'ttouch with power on - it is at over a hundred volts with nasty multihundredvolt spikes and line connected - discharge power supply filter caps firstafter unplugging). If it is scorching hot after a few minutes, then youneed to check the other possibilities. It is also possible that a defective flyback - perhaps one shorted turn - wouldnot cause an immediate failure and only affect the picture slightly. Thiswould be unusual, however. See the section: "Testing of flyback (LOPT)transformers". Note that running the set with a series light bulb may allow the HOTto survive long enough for you to gather some of the information neededto identify the bad component. Horizontal output transistors blowing at random intervals:--------------------------------------------------------- The HOT may last a few months or years but then blow again. These are among the hardest problems to locate. It could even be some peculiarcombination of user cockpit error - customer abuse - that you will neveridentify. Yes, this should not happen with a properly designed monitor.However, a combination of mode switching, loss of sync during bootup, runningon the edge of acceptable scan rates, and frequent power cycles, could testthe monitor in ways never dreamed of by the designers. It may take only onescan line that is too long to blow the HOT. Vertical foldover:----------------- The picture is squashed vertically and a part of it may be flipped over anddistorted. This usually indicates a fault in the vertical output circuit. If it usesan IC for this, then the chip could be bad. It could also be a bad capacitoror other component in this circuit. It is probably caused by a fault in the flyback portion of the vertical deflection circuit - a charge pump thatgenerates a high voltage spike to return the beam to the top of the screen. Test components in the vertical output stage or substitute for good ones. Comments on vertical problems:----------------------------- (From: Bert Christensen (bert.christensen@rose.com)). As a general rule, vertical faults can be divided into two types: ones thatcause geometric distortion (a circle will not be round) and those that simplyblack out a portion of the screen. The former are faults in the verticaloscillator, drive, or output stages. The latter are blanking faults. Blankingfaults are almost always caused by electrolytic capacitors changing value andthereby changing the timing of the pulses which blank the screen duringvertical retrace. In other words, the pulses are turning off the video signalsat the wrong time. The most common true vertical fault is geometric distortion and a foldover ofwhite lines at the top of the screen. This is almost always caused by theelectrolytic capacitor on or near the collector of the vertical outputtransistor or part of the IC which has the supply voltage (B+) on it. In theold tube days, the general rule was that bottom distortion was in the cathodeof the output tube and distortion at the top was caused by a fault in thedrive circuit. Excessive width/pincushioning problems:-------------------------------------- This would mean that the left and right sides of the picture are 'bowed' andthe screen looks something like the diagram below (or the opposite - barreldistortion). However, the obvious symptoms may just be excess width as the curved sides maybe cut off by the CRT bezel. ============================================ \ / \ / \ / \ / \ / \ / / \ / \ / \ / \ / \ / \============================================== In particular, this sounds like a pincushion problem - to correct forpincushion, a signal from the vertical deflection that looks somethinglike a rectified sinewave is used to modify width based on vertical position.There is usually a control to adjust the magnitude of this signal and alsooften, its phase. It would seem that this circuit has ceased to function. If you have the schematics, check them for 'pincushion' adjustments andcheck signals and voltages. If not, try to find the 'pincushion' magnitudeand phase adjustments and look for bad parts or bad connections in in thegeneral area. Even if there are no adjustment pots, there may still bepincushion correction circuitry. If the internal controls have absolutely no effect, then the circuitis faulty. With modern digital setup adjustments, then it is even tougherto diagnose since these control a D/A somewhere linked via a microprocessor. Pincushion adjustment adds a signal to the horizontal deflectionto compensate for the geometry of the CRT/deflection yoke. If you haveknobs, then tracing the circuitry may be possible. With luck, you havea bad part that can be identified with an ohmmeter - shorted or open.For example, if the pincushion correction driver transistor is shorted,it will have no effect and the picture will be too wide and distorted asshown above. However, without a schematic even this will be difficult. If the adjustmentsare digital this is especially difficult to diagnose since you don't evenhave any idea of where the circuitry would be located. Faulty capacitors in the horizontal deflection power supplies often causea similar set of symptoms. Deflection yoke testing:----------------------- A faulty deflection yoke can affect the geometry (size and shape) of theraster, result in insufficient high voltage and/or other auxiliary powerproblems, and blow various components in the low voltage power supply orelsewhere. * A simple test to determine if the yoke is at fault for a major geometry problem (e.g., a keystone shaped picture) is to interchange the connections to the yoke for the axis that is not affected (i.e., the vertical coils if the width is varying from top to bottom). If the raster/picture flips (indicating that you swapped the proper connections) but the shape of the raster remains the same - the geometry is unchanged, the problem is almost certainly in the deflection yoke. * Where high voltage (and other flyback derived voltages) are reduced and other problems have been ruled out, unplugging the deflection yoke (assuming no interlock) may reveal whether it is likely at fault. If this results in high voltage and a relatively clean deflection waveform or returns the power supply or deflection chip load to something reasonable, a defective yoke is quite possible. CAUTION: powering a TV or monitor with a disconnected yoke must be done with care for several reasons: - The CRT electron beam(s) will not be deflected. If it turns out that the yoke is the problem, this may result in a very bright spot in the center of the screen (which will turn into a very dark permanent spot quite quickly) :-(. Disconnecting only the winding that is suspect is better. Then, the other direction will still scan resulting in a very bright line instead of a super bright spot. In any case, make sure the brightness is turned all the way down (using the screen/G2 control on the flyback if necessary). Keep an eye on the front of the screen ready to kill power at the first sign of a spot or line. Disconnecting the CRT heater as an added precaution would be even better unless you need to determine if there is a beam. - Removing the yoke (which is effectively in parallel with the flyback) increases the inductance and the peak flyback voltage on the HOT. In the extreme, this may blow the HOT if run at full line voltage/normal B+. It is better to perform these tests using a Variac at reduced line voltage if possible. - The deflection system will be detuned since the yoke inductance plays a very significant role in setting the resonance point in most designs. Don't expect to see totally normal behavior with respect to high voltage. However, it should be much better than with the faulty yoke. * If possible, compare all measurements with a known good identical deflection yoke. Of course, if you have one, swapping is the fastest surest test of all! In many cases, even a not quite identical yoke will be close enough to provide useful information for testing. However, it must be from a similar piece of equipment with similar specifications - size and scan range. Don't expect a color TV yoke to work in a high performance SVGA monitor! Note: the substitute yoke doesn't have to be mounted on the CRT which would disturb purity and convergence adjustments but see the caution above about drilling holes in the CRT face plate! The deflection yoke consists of the horizontal coils and vertical coils (woundon a ferrite core), and mounting structure. Little magnets or rubber/ferritestrips may be glued in strategic locations. DO NOT disturb them! In rareinstances, there may be additional coils or other components mounted on thesame assembly. The following deals only with the actual deflection coilsthemselves - the other components (if any) can be tested in a similar manner. Where the test procedure below requires removal of the yoke, see the section:"Removing and replacing the deflection yoke" first. * Horizontal - the horizontal section consists of an even number of windings hooked up in parallel/interleaved with half of the windings on each of the two ferrite core pieces. The horizontal windings will be oriented with the coil's axis vertical and mounted on the inside of the yoke (against the CRT neck/funnel). It may be wound with thicker wire than that used for the vertical windings. - Resistance check - This may be possible without removing the yoke from the CRT if the terminal block is accessible. Disconnect the individual windings from each another and determine if the resistances are nearly equal. Check for shorts between windings and between the horizontal and vertical windings as well. Typical resistance of the intact windings (at the yoke connector assuming no other components): TV or NTSC/PAL monitor - a few ohms (3 ohms typical), SVGA monitor - less than an ohm (.5 ohms typical). - Inspection - Look for charring or other evidence of insulation breakdown due to arcing or overheating. For the horizontal windings, this will require removing the yoke from the CRT since little if any of the windings are visible from the outside. However, even then, most of the windings are hidden under layers of wire or behind the ferrite core. - Ring test. See the document "Testing of Flyback (LOPT) Transformers". This deals with flyback transformers but the principles are the same. Disconnecting the windings may help isolate the location of a fault. However, for windings wound on the same core, the inductive coupling will result in a short anywhere on that core reducing the Q. * Vertical - The vertical section is usually manufactured as a pair of windings wired in parallel (or maybe in series) though for high vertical scan rate monitors, multiple parallel/interleaved windings are also possible. The vertical windings will be oriented with the coil's axis horizontal and wound on the outside of the yoke. The wire used for the vertical winding may be thinner than that used for the horizontal windings. - Resistance check - This may be possible without removing the yoke from the CRT if the terminal block is accessible. Disconnect the individual windings from each other and determine if the resistances are nearly equal. Check for shorts between windings and between the horizontal and vertical windings as well. Typical resistance of the intact windings (at the yoke connector assuming no other components): TV or NTSC/PAL monitor - more than 10 ohms (15 ohms typical), SVGA monitor - at least a few ohms (5 ohms typical). - Inspection - Look for charring or other evidence of insulation breakdown due to arcing or overheating. The accessible portions of the vertical windings are mostly visible without removing the yoke from the CRT. However, most of the windings are hidden under layers of wire or behind the ferrite core. - Ring test - Since the vertical windings have significant resistance and very low Q, a ring test may be of limited value. Deflection yoke repair:---------------------- So you found a big black charred area in/on one of the yoke windings. Whatcan be done? Is it possible to repair it? What about using it for testingto confirm that there are no other problems before ordering a new yoke? If the damage is minor - only a few wires are involved, it may be possible toseparate them from each other and the rest of the winding, thoroughly cleanthe area, and then insulate the wires with high temperature varnish. Then,check the resistances of each of the parallel/interleaved windings to makesure that you caught all the damage. Simple plastic electrical tape can probably be used for as insulation fortesting purposes - it has worked for me - but would not likely survive verylong as a permanent repair due to the possible high temperatures involved.A new yoke will almost certainly be needed. Testing of flyback (LOPT) transformers:-------------------------------------- How and why do flyback transformers fail? Flybacks fail in several ways: 1. Overheating leading to cracks in the plastic and external arcing. These can often be fixed by cleaning and coating with multiple layers of high voltage sealer, corona dope, or even plastic electrical tape (as a temporary repair in a pinch). 2. Cracked or otherwise damaged core will effect the flyback characteristics to the point where it may not work correctly or even blow the horizontal output transistor. 3. Internal shorts in the FOCUS/SCREEN divider network, if present. One sign of this may be arcover of the FOCUS or SCREEN sparkgaps on the PCB on the neck of the CRT. 4. Internal short circuits in the windings. 5. Open windings. More than one of these may apply in any given case. First, perform a careful visual inspection with power off. Look for cracks,bulging or melted plastic, and discoloration, Look for bad solder connectionsat the pins of the flyback as well. If the TV or monitor can be poweredsafely, check for arcing or corona around the flyback and in its vicinity, Next, perform ohmmeter tests for obvious short circuits between windings,much reduced winding resistances, and open windings. For the low voltage windings, service manuals may provide the expectedDC resistance (Sams' PhotoFact, for example). Sometimes, this will changeenough to be detected - if you have an ohmmeter with a low enough scale.These are usually a fraction of an ohm. It is difficult or impossible tomeasure the DC resistance of the HV winding since the rectifiers are usuallybuilt in. The value is not published either. Caution: make sure you have the TV or monitor unplugged and confirm thatthe main filter capacitor is discharged before touching anything! If youare going to remove or touch the CRT HV, focus, or screen wires, dischargethe HV first using a well insulated high value resistor (e.g., severalM ohms, 5 W) to the CRT ground strap (NOT signal ground. See the section:"Safe discharging of capacitors in TVs and video monitors". Partially short circuited windings (perhaps, just a couple of turns)and sometimes shorts in the focus/screen divider will drastically lowerthe Q and increase the load the flyback puts on its driving source withno outputs connected. Commercial flyback testers measure the Q bymonitoring the decay time of a resonant circuit formed by a capacitor anda winding on the flyback under test after it is excited by a pulsewaveform. It is possible to easily construct testers that perform awell. See the companion document "Testing of Flyback (LOPT) Transformers"for further information. ***************** High Voltage Power Supply Problems ***************** HV power supply fundamentals:---------------------------- Most, if not all, TVs derive the high voltage for the CRT second anode,focus, and (sometimes) screen (G2) from the horizontal deflection system.This technique was developed quite early in the history of commercial TVand has stuck for a very simple reason - it is very cost effective. Aside effect is that if the horizontal deflection fails and threatens toburn a (vertical) line into the CRT phosphors, the high voltage dies as well. Most TV high voltage supplies operate as follows: 1. Horizontal output transistor (HOT) turns on during scan. Current increases linearly in primary of flyback transformer since it appears as an inductor. Magnetic field also increases linearly. Note: flyback is constructed with air gap in core. This makes it behave more like an inductor as far as the primary drive is concerned. 2. HOT shuts off at end of scan. Current decreases rapidly. Magnetic field collapses inductively coupling to secondary and generates HV pulse. Inductance and capacitance of flyback, snubber capacitors, and parasitic capacitance of circuitry and yoke form a resonant circuit. Ideally, voltage waveform across HOT during flyback (retrace) period will be a single half cycle and is clamped by damper diode across HOT to prevent undershoot. 3. Secondary of flyback is either a single large HV winding with HV rectifiers built in (most often) or an intermediate voltage winding and a voltage multiplier built in or a separate unit (see the section: "What is a tripler?".) The output will be DC HV pulses. 4, The capacitance of the CRT envelope provides the needed filtering to adequately smooth the HV pulses into a DC voltage. 5, A high resistance voltage divider provides the several KV focus voltage and sometimes the several hundred volt screen (G2) voltage as well. Often, the adjustments for these voltages are built into the flyback. Sometimes they are mounted separately. The focus and screen are generally the top and bottom knobs, respectively. What is a tripler?:------------------ In some TVs, the flyback transformer only generates about 6-10 KV AC whichis then boosted by a diode-capacitor ladder to the 18-30 KV needed for moderncolor CRTs. The unit that does this is commonly called a tripler since itmultiplies the flyback output by about 3 times. Some TVs use a quadruplerinstead. However, many TVs generate the required HV directly with a windingwith the required number of turns inside the flyback transformer. Triplers use a diode-capacitor ladder to multiply the 6-10 KV AC to 18-30 KVDC. Many triplers are separate units, roughly cubical, and are not repairable.Some triplers are built in to the flyback - it is probably cheaper tomanufacture the HV diodes and capacitors than to wind a direct high voltagesecondary on the flyback core. In either case, failure requires replacement of the entire unit. For external multipliers, the terminals are typically marked: IN - from flyback (6-10 KV AC). OUT - HV to CRT (20-30 KV DC). F - focus to CRT (2-8 KV). CTL - focus pot (many megohm to ground). G, GND, or COM - ground. Symptoms of tripler failure are: lack of high voltage or insufficient highvoltage, arcing at focus protection spark gap, incorrect focus voltage, otherarcing, overload of HOT and/or flyback, or focus adjustment affectingbrightness (screen) setting or vice-versa. High voltage shutdown due to X-ray protection circuits:------------------------------------------------------ A TV that runs for a while or starts to come on but then shuts down mayhave a problem with the X-ray protection circuitry correctly or incorrectlydetermining that the high voltage (HV) is too great (risking excessiveX-ray emission) and shutting everything down. A side effect of activation of this circuitry is that resetting may requirepulling the plug or turning off the real (hard) power switch. Is there anything else unusual about the picture lately that would indicatean actual problem with the HV? If this is the case, then there may besome problem with the HV regulation. If not, the shutdown circuit maybe overly sensitive or one of its components may be defective - a badconnection of leaky cap (or zener). If the horizontal frequency is not correct (probably low) due to a faultyhorizontal oscillator or sync circuit or bad horizontal hold control (shouldone exist!), HV may increase and trigger shutdown. Of course, the picturewon't be worth much either! One symptom of excessive HV (but not required) is an overly bright pictureof reduced size. The HV shutdown circuit usually monitors a winding off of the flybackfor voltage exceeding some reference and then sets a flip flop shuttingthe horizontal drive off. On some Sony models, a HV resistive divider performs this function and thesedo fail - quite often. The big red Hstat block is a common cause of immediateor delayed shutdown on certain Sony monitors and TVs. See the section: "SonyTVs/monitors and Hstat". Low or no high voltage:---------------------- Most of these problems are due to faults in the horizontal deflectionsystem - shorted HOT, shorted windings or HV rectifiers in the flyback,defective tripler, or other bad parts on the primary side of the flyback. However, if you discover an inch layer of filth inside the TV, the HVcould simply be shorting out - clean it first. In most cases, these sorts of faults will put an excessive load on thehorizontal output circuits so there may be excessive heating of the HOTor other components. You may hear an audible arcing or sizzling sound frominternal shorts in the flyback or tripler. Either of these may bet hot,crack, bulge, or exhibit visible damage if left on with the fault present. Most modern TVs do not regulate HV directly but rather set it viacontrol of the low voltage power supply to the HOT (B+), by snubbercapacitors across the HOT, and the turns ratio of the flyback. TheHV is directly related to the B+ so if this is low, the HV will be lowas well. Faulty snubber capacitors will generally do the opposite - increasethe HV and the X-ray protection circuits may kick in. However, low HVis also a possibility. The only way the turns ratio of the flyback canchange is from a short which will manifest its presence in other ways aswell - excessive heating and load on the horizontal output circuits. While a shorted second anode connection to the CRT is theoreticallypossible, this is quite unlikely (except, as noted, due to dirt). Excessive high voltage:---------------------- Any significant increase in HV should cause the X-ray protection circuitsto kick in and either shut down the set or modify the deflection in sucha way as to render it harmless. Symptoms include arcing/sparking of HV, smaller than normal picture, andunder certain scenarios, possible excessive brightness. Causes of the HV being too high are: 1. Excess B+ voltage to the HOT. The likely cause is to a low voltage regulator failure. 2. Open snubber capacitors across the HOT. These are under a lot of stress and are located near hot components so failure is possible. 3. Incorrect excessively long scan drive to HOT caused by failure of horizontal oscillator/sync circuits. However, other things like the HOT will probably blow up first. The picture will definitely be messed up. 4. Failure of HV regulator (tube sets and a few solid state sets - actual HV regulators are relatively uncommon today.) This may result in an underscanned (smaller than normal) picture. Snaps, crackles, and other HV breakdown:--------------------------------------- Various problems can result in occasional or sustained sparking or arcingsounds from inside the monitor. Note that a static electricity buildupis common on the front of the screen. It is harmless and there iss nothingyou can do about it anyhow. The following may result in occasional or sustained sounds not commonlyassociated with a properly working TV or monitor. There may or may not beflashes or blanking of the screen at the same time as the audible noise.See the same-named sections that follow for details. * Arcing, sparking, or corona from CRT HV anode (red wire/suction cup). * Arcing at CRT sparkgaps. * Arcing from flyback or vicinity. * Arcing due to bad connections to or disconnected CRT return. * Flashovers inside the CRT. Arcing, sparking, or corona from CRT HV anode (red wire/suction cup):-------------------------------------------------------------------- Symptoms could include a sizzling corona or more likely, an occasionalor rapid series of sharp snaps - possibly quite loud and quite visible - fromthe anode connection (at the suction cup) on the CRT to the grounded coatingon the outside of the CRT or a chassis ground point (or any other conductornearby). Corona is a high resistance leakage through the air without totalbreakdown. The snapping is caused by the sudden and nearly complete dischargeof the CRT anode capacitance through a low resistance ionized path similar tolightning. There are two likely causes: 1. Dirt, dust, grime, around and under the suction cup on the CRT are providing a discharge path. This may be more severe in humid weather. Safely discharge the HV and then remove and thoroughly clean the HV suction cup and the area under it and on the CRT for several inches around the HV connection. Make sure there are no loose wires or other possible places for the HV to discharge to in the vicinity. 2. The high voltage has gone through the roof. Usually, the X-ray protection circuitry should kick in but it can fail. If cleaning does not help, this is a likely possibility. See the sections: "High voltage shutdown due to X-ray protection circuits" and "Excessive high voltage". Arcing from flyback or vicinity:------------------------------- Arcing may be visible or audible and result in readily detectable levelsof ozone. Note that very slight traces of ozone may not indicate anythingsignificant but if the TV smells like an office copier, there is probablysome discharge taking place. WARNING: It is possible for arcing to develop as a result of excessive highvoltage. Symptoms might be a smaller than normal excessively bright picturebut this may not be able to be confirmed until the flyback is repaired orreplaced. See the section: "Excessive high voltage". * On the HV output, it will probably be a loud snapping sound (due to the capacitance of the CRT) with associated blue/white sparks up to an inch or more in length. If the arc length is short enough, this may turn into a nearly continuous sizzling sound with yellow/orange arc and melting/burning plastic. * Prior to the HV rectifier, it will likely be a continuous sizzle with orange/yellow/white arc and melting/burning plastic or circuit board material. * Internal arcing in the flyback may be audible and eventually result in a bulging and/or cracked case (if some other component doesn't fail first as this would take some time to develop). * A corona discharge without actual sparks or a visible well defined arc is also possible. This may be visible in a totally dark room, possibly more likely when the humidity is high. A thorough cleaning to remove all dust and grime may be all that is needed in this case. * If the arc is coming from a specific point on the flyback - a crack or pinhole - this may be patched well enough to confirm that the rest of the TV is operational and a new flyback is worth the money. Otherwise, there is no way of knowing if the arcing may have damaged other circuitry until a replacement flyback - possibly money wasted - arrives. To attempt a repair, scrape off any dirt or carbon that is present along the path of the arcing and its vicinity. Then, clean the area thoroughly with alcohol and dry completely. Otherwise, the dirt and carbon will just act as a good conductor and the arcing will continue under your repair! Several layers of plastic electrical tape may be adequate for testing. Multiple coats of high voltage sealer or non-corroding RTV silicone (if it smells like viniger - acetic acid - as it cures, this may get in and affect the windings) would be better if the objective is an actual repair. This may prove to be a permanent fix although starting the search for a source for a new flyback would not hurt just in case. The arc most likely did damage the insulation internally which may or may not be a problem in the future. Also see the section: "Dave's complete procedure for repair of an arcing flyback". * In some cases, the pinhole or crack is an indication of a more serious problem - overheating due to shorted windings in the flyback or excessive secondary load. * If the arc is from one of the sparkgaps around the CRT or the CRT socket, this could also be a flyback problem indicating internal shorts in the focus/screen network. * If the arcing is inside the CRT, this could indicate a bad CRT or a problem with the flyback focus/screen network and no or inadequate sparkgap protection. Where repair seems possible, first, clean the areas around the arc thoroughlyand then try several layers of plastic electrical tape. If the TV worksnormally for say, an hour, then there is probably nothing else wrong and youcan try for a proper sealing job or hope that tape holds out (put a few morelayers on - each is good for about 8-10 KV theoretically). However, replacement of the flyback really is the best alternative to minimizerisk of future problems. This is the only option where there could be apotential issue of liability should subsequent failure result in a fire. Once I had a TV where the main problem was a cracked flyback arcingbut this took out one of the fusable resistors for the power supply tothe *vertical* output so the symptoms included a single horizontal line.Don't ask me to explain - replacing that resistor and the flyback (theflyback tested good, but this was for someone else) fixed the TV. In another case, a pinhole developed in the flyback casing probablydue to poor plastic molding at the time of manufacture. This resulted ina most spectacular case of sparking to a nearby bracket. A few layers ofelectrical tape was all that was needed to affect a permanent repair. Dave's complete procedure for repair of an arcing flyback:--------------------------------------------------------- (From: Dave Moore (penguin@datastar.net). First I clean the afflicted area with Electromotive spray from Autozone. It'sfor cleaning alternators. On Z-line I remove the focus control and wash withthe alternator cleaner and a tooth brush until all dirt and carbon depositsare removed. Then I take an xacto knife and carve out the carbonized holewhere the arcing broke through. Then take your soldering iron and close thehole by melting adjacent plastic into it. (clean any solder off your iron withsolder-wick first). Then cut some plastic off of some other part off theflyback where it wont be needed and use this to plastic weld (with your iron)a hump of a patch into and over the arc hole. Smooth and seal with iron. Nextapply as thick a layer of silicone rubber as you can and let dry overnight. Arcing at spark gaps and gas discharge tubes on CRT neck board or elsewhere:--------------------------------------------------------------------------- These are protective devices intended to breakdown and divert excessive voltageaway from the CRT (usually). This is rarely due to a defective sparkgap or gas discharge tube but rather isa safety mechanism like a fuse designed to protect the internal electrodes ofthe CRT if the focus or screen voltage should become excessive. The sparkgapbreaks down first and prevents internal arcing in the CRT. These sparkgapsmay be built into the CRT socket as well. Arcing at a sparkgap or a glowing or flashing discharge tube may be accompaniedby total loss of picture or bad focus, brightness or focus fluctuations, orany of a number of similar symptoms. A common cause is a breakdown inside thefocus divider (usually part of the flyback or tripler) but could also be due toexcessive uncontrolled high voltage due to a failure of the B+ regulator or HOTsnubber capacitor, or (ironically) even a short inside the CRT. * Spark gaps may be actual two or three pin devices with seemingly no insides, part of the CRT socket, or printed on the circuit board itself. * Gas discharge tubes look like small neon lamps (e.g., NE2) but could be filled with some other gas mixture to provide a controlled higher breakdown voltage. Therefore, like a fuse, don't just replace or disable these devices, locate andcorrect underlying problem. The CRT makes an expensive fuse! Arcing due to bad connections to or disconnected CRT return:----------------------------------------------------------- The Aquadag coating on the outside of the CRT is the negative plate of the HVfilter capacitor. If this is not solidly connected to the HV return, you willhave your 25 KV+ trying to go where it should not be. There should be a wiresolidly attached to the CRT neck board or chassis. Without this, voltage willbuild up until it is able to take some other path - possibly resulting indamage to sensitive solid state components in the process. Therefore, is isimportant to rectify the situation. Warning: If you find this disconnected, don't just attach it anywhere. Youmay instantly kill ICs or other solid state components. It must be connectedto the proper return point on the CRT neck board or chassis. Flashovers inside the CRT:------------------------- Due to sharp edges on the electron gun electrodes, impurities, and othermanufacturing defects, there can be occasional arcing internal to theCRT. Properly designed HV, deflection, and power supply circuits candeal with these without failing but not all monitors are designed well. There is nothing you can do about flashovers assuming your HV is notexcessive (see the section: "Excessive high voltage". If these persistand/or become more frequent, a new CRT or new TV will be needed. Ozone smell and/or smoke from TV:-------------------------------- Smoking is just as bad for TVs as for people and usually more quicklyterminal. White acrid smoke may indicate a failed electrolytic capacitor in thepower supply probably in conjunction with a shorted rectifier. Needless tosay, pull the plug at once. A visual inspection should be able to easily confirm the bad capacitor as itwill probably be bulging and have condensed residue nearby. Check therectifier diodes or bridge rectifier with an ohmmeter. Resistance acrossany pair of leads should be more than a few ohms in at least one direction.Remove from the circuit to confirm. Both the faulty diode(s) and capacitorshould be replaced (though the capacitor may work well enough to testwith new diode(s). If a visual inspection fails to identify the smoking part, you can probablyplug the set in for a few seconds until the source of the smoke is obviousbut be prepared to pull the plug in a real hurry. If the smell/smoke is coming from the flyback, then it has probably gonebelly up. You may be able to see a crack or bulge in the case. Whilethe flyback will definitely need to be replaced, it is likely that nothingelse is wrong. However, it might be prudent to use a Variac when performinginitial testing with the replacement just in case there is a secondaryshort circuit or excess HV problem. X-ray and other EM emission from my monitor?:-------------------------------------------- X-ray radiation is produced when a high velocity electron beam strikesa target containing heavy metals. In a modern monitor, this can onlytake place at the shadow mask/aperture grille and phosphor screen of the CRT. For X-rays, the amount of radiation (if any) will be proportional tobrightness. The energy (determined by the CRT high voltage, called KVPin the medical imaging field) is not affected. This is one reason manymonitors and TVs are designed with brightness limiting circuits. In any case, there will be virtually no X-ray emissions from the front ofthe CRT as the glass is greater than an inch thick and probably containssome lead for added shielding. Also see the section: "Should I be worriedabout X-ray exposure while servicing a TV or monitor?". Electromagnetic radiation (EM) is produced mostly from the deflection yokeand to a lesser extent from some of the other magnetic components liketransformers and inductors. Depending on monitor design (some arespecifically designed to reduce this), EM emissions can vary quite a bit.Frequencies range from the 50/60 Hz of the power line or vertical scan rateto several hundred KHz in the AM broadcast band. The intensity and spectraldistribution will vary depending on horizontal and vertical scan rate. A totally black screen will reduce X-ray emission to zero. It will notaffect EM emissions significantly as most of this comes from the magneticparts, particularly the deflection yoke. There is no measurable microwave, IR, or UV radiation. I refuse to get into the discussion of what, if any, health problems resultfrom low level EM emissions. There is simply not enough data. Should I be worried about X-ray exposure while servicing a TV or monitor?:------------------------------------------------------------------------- The only source of X-rays in a modern TV or monitor is from the CRT. X-raysare generated when a high velocity electron beam strikes a heavy metal target.For anything you are likely to encounter, this can only happen in a vacuum -thus inside the CRT. The higher the voltage, the greater the velocity andpotential danger. Really old TVs (prior to around 1975) may still have HVrectifier and regulator tubes - other sources of X-rays. However, modern TVsand monitors implement these functions with solid state components. The thick front CRT faceplate protects users adequately but there may be someemission from the thinner sides. At 25-30 KV (quite low as X-ray energies go)X-rays will be stopped by almost any metal so what you have to worry aboutis where there are no shields. However, realistically, there is very little danger. I would not worry aboutexposure unless you plan to be sitting for hours on the sides, behind, orunder the TV or monitor - with a picture (there will be none if the screen isblack). It is interesting that even those 1.5" Watchman and .5" camcorder viewfinderCRTs have X-ray warning labels even though the high voltage used with theseisn't anywhere near high enough to be of any concern! Flyback shot by 4 year old with water pistol:-------------------------------------------- Your 4 year old son shot the Sony in the flyback transformer. Smoke and sparkseverywhere. Great aim! Who says these FAQs cannot be funny? Needless to say, unplug the set immediately. Inspect around the targetarea for obviously blown or damaged components. Test fuses and fusableresistors. Repair burnt solder connections and circuit board traces.Once the set is entirely dried out, power it up - preferably through aseries light bulb and/or Variac until you are sure nothing else willlet loose. Look, listen, and smell for any unusual behavior. If itnow works, then consider yourself lucky. If not, there may be damageto transistors, ICs, or other components. (From: Richard Symonds (edison@nelson.planet.org.nz)). We're seeing another 'hazard' these days, people cleaning their televisionscreens with window cleaner - no problem in the days of separate chassis butwith the entire circuit board jammed under the tube on most TVs these daysjust a few drips and its all over. Some have just corroded the switch banks(had one recently just got into the A/V switch - when you walked around theroom the set changed to A/V and back by itself!) but a few have got around themicroprocessors and surface mount components and resulted in completewrite-offs. I suppose the damage is the opposite of electroplating as themicroprocessors have constant voltage to them. Never mind, they'll be a goodsource of parts for future use. Blooming or breathing problems:------------------------------ There are several symptoms that are basically similar: * Blooming is defined as an expansion of the raster or horizontal sections of the raster with bright material. For example, switching between dark and light picture causes the size of the picture to expand by 10%. A slight change in size is unavoidable but if it is greater than 1 or 2 percent from a totally black image to a full white one, this is either an indication of a defective TV or one that is badly designed. The cause is poor low or high voltage regulation. Check the B+ to the horizontal deflection. This is usually well regulated. If it is varying in sympathy to the size changes, trace back to determine why the low voltage regulator is not doing its job. The reason for the size change is that the high voltage is dropping and reducing the stiffness of the electron beam. * Expansion of the raster width in areas of bright imagery is an indication of short term regulation problems. The video drive may be interacting with the other power supplies. Check for ripple - this would be at the vertical scan rate - in the various regulated power supplies. The cause may be a dried up electrolytic capacitor - once you locate the offending voltage, test or substitute capacitors in that supply. In both these cases, if this just started after some work was done to the TV,the brightness limiter and/or video drive may simply be set so high that theTV cannot supply enough current to the high voltage. If the brightnessis acceptable with these turned down slightly and still have acceptablebrightness, then there may be nothing wrong. * Breathing is defined as a periodic change in the size of the raster which may be independent of what is displayed or its severity or frequency may be related to the brightness or darkness of the image. This is another type of regulation problem and may be caused by bad electrolytic capacitors or other components in the low voltage power supplies. If the TV uses a switchmode power supply or low voltage regulator separate from the horizontal deflection, first check its output(s) for a variation in voltage at the breathing rate. Test with a light bulb or resistor load to confirm that the problem is here and not the deflection or other subsystem of the TV. * A condition with somewhat similar symptoms is bad focus - fuzzy picture - but only with bright (high beam current) scenes. This could be just a matter of adjusting the focus control but may also indicate sub-optimal filament voltage due to bad connections or components in the filament circuit, or a tired worn CRT. You won't get high beam current without some serious spot blooming (a fat beam because too much cathode area is used) and you will get cathode 'poisoning' after prolonged use. Visually inspect the neck of the CRT for the normal orange glow of the filaments and check for bad connections and bad parts. Erratic focus or screen (G2) voltage and/or controls on flyback:------------------------=-------------------------------------- Symptoms may include fluctuating focus or brightness. In extreme cases,the result may be a too bright or dark picture or other behavior causedby breakdown in the Focus/Screen(G2) divider network. Usually, this will require flyback replacement to repair reliably. Sometimes,the section with the controls can be snapped apart and cleaned but this is notcommon. First, just try rotating the screen (G2) control back and forth a few times.This may clean up the contacts and eliminate the erratic behavior. Possibly,positioning it a bit to one side of the original location will help. Then,use the individual or other master background/bias adjustments to compensatefor the improper brightness. If pressing in on the erratic control helps to stabilize the setting, youmight try adjusting it to the optimal position and then put a dab of hot-meltglue (or Superglue if you can manage not to stick your fingers together) onthe shaft to hold it with a little more contact force. If none of this helps, here is a 'well it's going in the dumpster anyhow'procedure to try: After discharging the CRT (so you don't get zapped) drill a tiny hole inthe plastic cover near the bad control. Be careful you don't damage anythinginside - you just want access to the contacts of the controls. Use a handdrill with, say, a 1/16" bit. Don't drill more than about 1/8" deep whichshould enter the airspace. Then spray some contact cleaner through thehole and work the controls. Wait sufficient time (say, 24 hours) foreverything to dry COMPLETELY and see if behavior changes (or it works at all). This is a 'you have got to be kidding' type of repair so no guarantees :-). If by some miracle it does work, fill the hole with a drop of RTV or justput a couple of layers of electrical tape over it. Focus/Screen divider bypass surgery:----------------------------------- This is kludge number 41256 but may be the difference between a bit more lifeand the dumpster. If the previous extreme measures don't help, then it may be possible to simplysubstitute a good divider network externally. Note that if there is evidence of internal breakdown in the divider of theoriginal flyback (hissing, cracks, overheating, bulging case, etc.), this willnot work unless you can disconnect it from its HV connection. There are two issues: 1. Is this a stable situation? Even if you provide an external substitute, the parts inside the flyback may continue to deteriorate eventually resulting in other more total failure of the flyback or worse. 2. If you provide an external focus/screen divider, it must be done is such a manner (including proper mounting and super insulation) such that it cannot be called into question should there be a fire where the monitor is even the slightest bit suspect. Various size external focus/screen divider networks can be purchased butwhether this is truly a cost effective solution is not obvious. (From: Larry Sabo (sabo@storm.ca)). I just ordered a 'bleeder resistor' from Data Display Ltd (Canadian sub ofCCS) to use as a cure for flybacks with flaky focus/screen pots. It containsfocus and screen pots, and costs Cdn$ 16.99, which is a lot less than acomplete flyback, that's for sure. I expect it will be compatible with quite awide range of flybacks. I have used bleeder resistor assemblies from duff flybacks a couple of timeswith good success. You connect the HV lead into the HV cap of the originalflyback, ground all pins of the sub flyback, and use the focus and screenleads from the sub bleeder assembly in place of the originals. Looks like hell but works fine. Mounting (and securing) the substitute is achallenge given the limited space available. I only use this approach on whatwould otherwise be uneconomical to repair, and always advise the owner orcustomer of the cobbling job. It also enables you to verify whether it isthe flyback that needs replacement, versus the CRT. Decaying or erratic focus or screen (G2) voltages:------------------------------------------------- The following applies to both CRT focus voltage (which should be a few KV)and screen or G2 voltage (which should be several hundred V). "The screen voltage will come up to normal after sitting over night, 400 V or so. After approximately 5 minutes or slightly longer, I hear a slight arcing. From that point on, the screen voltage will wander anywhere from 75 V up to maybe 150 V. Adjustment of the screen control on the flyback has only a small effect and is not permanent. Removing the CRT pcb results in the screen voltage returning to normal." This is very likely a short between electrodes inside the CRT unless thereis something on the neck board that is breaking down as a result of someconnection to the CRT. The flyback should largely not know the differencewith the socket plugged into the CRT. One possibility is that glue used to hold components down on some circuitboards has deteriorated and turned conductive. Check for tan to brownstuff shorting traces on the CRT neck board. If this is present on thefocus or screen traces or wires, it may just be your problem. Scrape offall of the old glue and then clean thoroughly. Repair any damaged traces. What happens to the HV? A HV breakdown possibly inside the CRT would resultin all the voltages being dragged down. What happens to the picture? If you connect a charged HV capacitor (guessing a couple hundred volts,a couple microfarads) between G2 and G1 or focus, you **will** know iftapping the neck results in a momentary short! I cannot predict whetherthis will be a temporary cure or permanent killer. See the section:"Rescuing a shorted CRT". Here is another thing to try: put a 100 M ohm or so resistor between SCREENand the CRT socket. This should not affect the behavior much until thefailure occurs. Then, check the voltage on both sides with a high impedancevoltmeter (1000 M). If the CRT is arcing, it will be much lower on the CRT side and will probably fluctuate. You can play similar games with focusvoltage. Disconnecting focus wire from CRT driver board:---------------------------------------------- In some cases, the focus wire - the not-so-fat wire from the flyback or focusdivider - may terminate directly in the CRT socket with no obvious means offreeing it should flyback replacement be needed. One alternative is simply to cut the wire in a location that is well away fromany place to short out, solder, and then do a most excellent job of insulatingthe splice. However, you may find that the cap on the CRT socket snaps off using a thinknife blade or screwdriver. The wire may be soldered or just pressed in placein such a way that pulling it out is difficult or impossible without removingthe cover. (From: Raymond Carlsen (rrcc@u.washington.edu)). The last one I worked on puzzled me for a few moments. See if you can see aspace between the little cup (where the wire enters the socket) and the socketitself. Pry up on the cap with a knife and it should pop right off. The wireis soldered to a pin under it. Don't apply heat for very long... you may meltthe socket. Focus or screen voltage drifts after warmup only when CRT is connected:---------------------------------------------------------------------- "I have a 3-5 yr old TV that loses screen voltage. I believe that the problem is specific to the CRT or the flyback, either one is a guess I'd rather be sure of prior to ordering a part. The screen voltage will come up to normal after sitting over night, 400 V or so. After approximately 5 minutes or slightly longer, I hear a slight arcing. From that point on, the screen voltage will wander anywhere from 75 V up to maybe 150 V. Adjustment of the screen control on the flyback has only a small effect and is not permanent. Removing the CRT pcb results in the screen voltage returning to normal. I cannot find the source of the arcing, as it happens quickly and I have always been on the other side of the set when it happens. I have replaced the crt socket, thinking the spark gap was arcing. I have checked the CRT for G1 and HK shorts on a sencore crt checker, it checks good, but I am aware that since it is an intermittent problem, that the checker probably will not catch it." This sounds like a CRT short unless there is something on the neck boardthat is breaking down. The Sencore may not provide the same high voltagesas normal screen (several hundred volts) or focus (several thousand volts).The flyback should largely not know the difference whether the screen orfocus electrode of the CRT is connected or not. The current should beneglegible. One possibility is that glue used to hold components down on some circuitboards has deteriorated and turned conductive. Check for tan to brownstuff shorting traces on the CRT neck board. If this is present on thefocus or screen traces or wires, it may just be your problem. Scrape offall of the old glue and then clean thoroughly. Repair any damaged traces. What happens to the HV? A HV breakdown possibly inside the CRT would resultin all the voltages being dragged down. What happens to the picture? If you connect a charged HV capacitor (guessing a couple hundred volts,a couple microfarads) between G2 and G1 or focus, you **will** know iftapping the neck results in a momentary short! I cannot predict whetherthis will be a temporary cure or permanent killer. Here is another thing to try: put a 100 M ohm or so resistor between SCREEN(or FOCUS) and the CRT socket. This should not affect the behavior muchuntil the failure occurs. Then, check the voltage on both sides with a highimpedance voltmeter (>1000 M). If the CRT is arcing, it will be much loweron the CRT side. ***************** Raster, Color, and Video Problems ***************** No color - black and white picture:---------------------------------- This means absolutely no color - equivalent to a black and white picture.Not even a hint of color. First, confirm that the source is actually in color - try another channelor input device. Next, check the settings of the color control - it may have accidentallybeen turned down. If your TV has some kind of automatic picture mode,try turning if off and adjusting the color control. Try adjusting finetuning if you have such a control and the problem is with a broadcastor cable transmission. At this point with a confirmed color signal source, there is a problemwith the chroma circuitry. Note that to the average person, the obvious question becomes: is my colorpicture tube bad? The answer is a definitive NO. It is virtually impossiblefor a defective CRT to cause a total loss of color. A defective CRT cancause a lack of a primary color - R, G, or, B or a short between two colorswhich will mess up the color but is not likely to result in a black and whitepicture. Some possibilities in no particular order: 1. Weak signal or defect in tuner/IF causing loss of signal strength. 2. Coler killer set too high (internal control) if it has one. 3. Defective part around the chroma chip/circuit. Faulty color oscillator. 4. Bad connections in area of chroma chip/circuit. 5. Defective chroma chip (don't suspect this first just because it is probably very expensive). A service manual or Sams', DMM, & scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. Try proddingthe main board around the chroma chip with an insulated tool to see ifyou can make the color come and go. I had one set where a $.02 resistor decided to open up causing just thisproblem - perfect BW picture, no color. Another had a coil with a broken wire. Saturated color but almost no brightness:---------------------------------------- This means you have lost the luminance input to the chroma decoder or finalvideo chip. A failure of the brightness limiter may result in similarsymptoms. A few common causes are: * Check the service switch (if any). Its contacts may be dirty and moving it back and forth a few times or using contact cleaner may be all that is needed. * Check for open high value resistors around the chroma decoder IC. * Check for open high value resistors in the brightness limiter circuit. With a scope and schematic (or even just a pinout for the chip), you should beable to trace the luminance signal to see where it is getting lost. This is also *not* a picture tube problme :-). Brightness control has no effect:-------------------------------- The following assumes that the picture is fine but the brightness isfixed - probably at too high a level. However, there could be severalinterrelated problems if a common supply voltage were missing, for example. If it is a knob, then it should be varying the control grid (G1) voltagesrelative to the cathodes (K) of the CRT. This is not likely to be a verycomplex circuit. If you do not have a schematic, I would start by tracingfrom the control, check continuity and solder connections. Check thecontrol itself for proper operation with an ohmmeter. A power supply goingto one side of the control (negative probably) may be missing. Tbe controlgrid voltage will end up on the little board on the neck of the CRT - checkthere as well for bad solder connections or open resistors. If brightness is a digital control, then you will need a schematic unlessthere is an obvious bad connection. One color is too weak or too strong:----------------------------------- If the problem is slight and/or has gradually gotten worse, this may justrequire an adjustment of the color brightness/background/bias and/or colorgain/drive controls inside the TV. See the section: "Color balanceadjustment". Note that if it is possible to obtain a good black and white picture with theuser color control set to its minimum, then this is not likely a problem withone of the primary color channels (red, green, or blue) but with the chromadecoding circuitry. Or, perhaps, you are just watching MTV! Even if it appears as though there is an excess, this may actually be areduction in one of the primary colors. For example, a magenta tinge isrepresents a reduction in the strength of the green signal. * Too high an intensity for one of the color channels will result in a tint of one of the primaries: red, green or blue. * Too low an intensity for one of the color channels will result in a tint of the complement of one of the primaries: yellow, cyan, or magenta. * Problems mainly in the shadows or dark areas of the picture usually represent a fault with brightness/bias/background. * Problems mainly in the highlights or bright areas of the picture usually represent a fault with the gain/drive. A color that that is now suddenly brighter or darker than normal resulting inincorrect color balance or a tint in the background could be due to a numberof causes: * Bad connections or bad component in video amplifier or on CRT neck board for that color. * Fault in chroma decoder. * Weak gun in CRT (reduced color). Psychodelic color:----------------- The means colors that are not normal and that adjustment of the usercontrols is not able to correct it so that all colors of the pictureare properly displayed at the same time. For example, you are unableto get any yellows or blues in scenes that should have these colors.. Make sure the user color and tint controls have not been accidentallyturned while cleaning or purposedly misadjusted by small (or large) kids. Perform the user setup described in the section: "User pictureadjustment". Confirm that the source is not a weird color video - try anotherchannel or a tape. Verify that this is not a missing color problem - one of the primary R, G,or B, has disappeared. If so, refer to the section: "Intermittent or missingcolors". Once these have been eliminated, you are left with thefollowing possibilities: 1. Defective part around the chroma chip/circuit. Misadjusted color oscillator. 2. Bad connections or short circuit in area of chroma chip/circuit. 3. Defective chroma chip (don't suspect this first just because it is probably very expensive). 4. Bad degauss circuit resulting in lack of degauss or abrupt termination of degauss current rather than smooth tail off. The CRT is not being properly demagnetized and color purity is totally messed up. 5. Bad CRT - the shadow mask has been damaged and it is impossible to properly adjust purity across the screen. A service manual or Sams', DMM, & scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. For (1)-(3),try prodding the main board around the chroma chip with an insulated toolto see if you can restore normal color. For (4) try manually degaussing(see the section: "Degaussing (demagnetizing) a CRT". If this clears upthe colors until at least when it is power cycled, then a degauss problemis likely. Something as simple as a bad resistor or inductor can be the cause - don'timmediately suspect the most expensive and difficult to replace part. No picture/dark picture/erratic picture:--------------------------------------- Remove the picture tube socket (carefully!) and clean the pins with finesandpaper and use contact cleaner on the socket. This source of badconnections can result in a variety of erratic symptoms. TV and Monitor Manufacturing Quality and Cold Solder Joints:----------------------------------------------------------- Any intermittent problems with monitors that cause random sudden changes inthe picture brightness, color, size, or position are often a result ofbad connections. Bad solder joints are very common in TVs and monitors due both to poor qualitymanufacturing as well as to deterioration of the solder bond after numerousthermal cycles and components running at high temperature. Without knowinganything about the circuitry, it is usually possible to cure these problemsby locating all bad solder connections and cleaning and reseating internalconnectors. The term 'cold solder joint' strictly refers to a solderconnection that was either not heated enough during manufacturing, wascooled too quickly, or where part pins were moved before the solder hada chance to solidify. A similar situation can develop over time withthermal cycling where parts are not properly fastened and are essentiallybeing held in by the solder alone. Both situations are most common withthe pins of large components like transformers, power transistors andpower resistors, and large connectors. The pins of the components havea large thermal mass and may not get hot enough during manufacturing. Also,they are relatively massive and may flex the connection due to vibrationor thermal expansion and contraction. To locate cold solder joints, use a strong light and magnifier and examinethe pins of large components for hairline cracks in the solder around thepin. Gently wiggle the component if possible (with the power off). Anydetectable movement at the joint indicates a problem. With the power on,gently prod the circuit board and suspect components with an insulatedtool to see if the problem can be effected. When in doubt, resolder any suspicious connections. Some monitors mayuse double sided circuit boards which do not have plated through holes.In these cases, solder both top and bottom to be sure that the connectionsare solid. Use a large enough soldering iron to assure that your solderconnection is solid. Put a bit of new solder with flux on every connectionyou touch up even if there was plenty of solder there before. Why can't TV manufacturers learn to solder properly?:---------------------------------------------------- I can think of several potential reasons - all solvable but at highermanufacturing cost. 1. Mass of large component leads (like shields) does not get adequately heated during manufacture leading to latent cold solder joints. While they may look ok, the solder never actually 'wetted' the heavy pins and therefore did not form a good mechanical or electrical bond. 2. Thermal cycles and differential thermal coefficients of circuit boards, traces, and solder. While it is not easy to do anything about the material properties, using plated through-holes or a similar mechanical via would greatly increase the surface area of the joint and prevent the formation of cracks. 3. Vibration. This is also directly related to the single sided circuit boards without plated through-holes to strengthen the joints. 4. Lack of adquate mechanical support (single sided circuit boards without plated through-holes (vias). I believe that the single most significantimprovement would come aboutby using plated trhough-holes but this would add to the cost and apparentlythe consumer is not willing to pay more for better quality and reliability!Some designs have used rivlets - mechanical vias instead of plated ones.While this is good in principle, the execution has often been flawed wherecold solder joints resulted between the rivlets and the circuit board tracesdue to lack of adequate process control. The Sony and RCA/GE tuner shield problem is interesting because thiscould have been solved years ago at essentially no additional cost asother manufacturers - and their own repair procedures - have proven. Intermittent or missing colors:------------------------------ This is a catch-all for some of the most common TV and monitor problems. * If gently whacking the set can make the color(s) come and go suddenly, then bad connections are probable. The most likely place for these are solder pads on the little circuit board on the neck of the CRT or even dirty CRT socket pins that are not making solid contact. Try prodding the CRT neck board with an insulated stick to see if you can affect the colors. Although not impossible, this is not likely to be a CRT problem. * If the color fades in and out with a delay of about 10-15 seconds, it is probably intermittent power to the CRT filament for that color and probably means a bad CRT since the three filaments are wired in parallel inside the CRT. One of the internal connections has come loose. Look in the neck of the CRT to make sure all three filaments are glowing orange. If one is out or goes on and off, toss the set. Replacing the CRT is probably not worth it. However, if they all go on and off together (all colors would be fading in and out though perhaps not quite in unison), then bad connections for the CRT filaments on the CRT neck board are indicated. To narrow down the problem: * Locate the output for the bad color on the video driver board on the neck of the CRT. This will probably read a significantly higher voltage than the corresponding pins for the good colors. A circuit problem is likely - probably on this board. * Test components on this board for the good and bad color channels. A shorted transistor or open resistor can kill one channel. Swap parts between good and bad colors to confirm. * Gently pull the CRT neck board off of the CRT and replace it. This will tend to clean the contacts. * Connect an output of the video/chroma circuit/chip that is working (i.e., a color that appears on the screen) to *all* three color drivers on the CRT neck board. - If you now get a more-or-less black and white picture (there may be a moderate color tint as the relative intensities of R,G,B may not be balanced), the problem is likely with the chroma decoder or its support circuitry. Note: the picture will be the intensity of only one color channel so it will not be quite *normal* in any case. - If you still have missing or messed up colors, the problem is on the CRT neck board or with the CRT. Most of the causes of intermittent colors boil down to bad connectionsof one form or another. For totally dead colors - not intermittent - badcomponents are also a possibility. * Printed circuit board on the CRT neck. This is a common location for cold solder joints. Check with a bright light and magnifying glass for hairline cracks around the pins of larger parts. Prod and tap with an insulated tool to see if the problem is effected. Resolder if necessary. * Cold solder joints elsewhere in TV or monitor usually around the pins of large parts such as transformers, power transistors and resistors, and internal connectors. * Internal connectors (including CRT socket) that need to be cleaned and reseated. Remove, clean with contact cleaner, burnish, and replace. Some commentary on monitor and TV whacking:------------------------------------------ Anytime that intermittent symptoms are experienced, I recommend gentlywhacking the patient to determine if mechanical shock or vibration affectsthe behavior. Here are a couple of responses to this suggestion. (The following is from Marc Gelfond (71363.1700@CompuServe.COM)): I just love the bit about "whacking it". It brings to mind an episode from the old Andy Griffith show, where a new fangled piece of electronics gear, was broght into Emmets repair shop. After many long hours of fruitless troubleshooting, out of frustration Emmet gave the thing a whack, and sure enough it fixed the problem. As we say in the Telephony business, it "CCWT" or Came Clear While Testing. Another saying is that it "CCBFM" Came Clear By F------ Magic!! (To which Gavin Adams (gaa@hopi.com) comments): In the video industry we had a saying concerning malfunctioning gear: "If it's broke, hit it with a hammer""If that doesn't fix it, paint it and sell it" My DEC 16" monitor is case in point. Evey once in a while it would lose sync,and smacking it would bring it back (sometimes a few smacks). Recently itgave up the ghost completely, and after the local DEC office gave me a quoteof $900 to fix it (Bermuda), I ordered a new Viewsonic 17" for the same price. I ripped the guts out of the DEC beast, painted it with a marble finish, putplants in it, and sold it! :> Retrace lines in picture:------------------------ During the time the electron beam is returning from right to left at the endof a line and bottom to top (over the course of multiple lines), it is supposedto be result in no visible light on the screen. However, a number of faultscan result in visible retrace lines. The appearance will likely be a general reduction in contrast from the visiblehorizontal retrace on every scan line and two dozen or so diagonal lines lines(lower left to upper right) resulting from the vertical retrace. The retrace lines may be either white or gray (possibly with a slight colortint due to unequal settings of the color adjustments) or a primary color -red, green, or blue. Anything in between is also possible but less likely. White/gray retrace lines:------------------------ Where all colors are involved - the lines are essentially white or gray (orwith a slight tint due to slight unequal settings of the color adjustments),look for something common like an incorrectly adjusted screen (G2) or masterbrightness/background/bias control or a problem in one of these circuits, adefective power supply or a problem in the blanking circuitry: * Screen (G2) or master brightness/background/bias control - mark setting and then see if a slight adjustment removes the retrace lines. See the chapter: "TV Adjustments". Of course, if this happened suddenly, the problem is not due to a misadjusted control though a dirty pot is possible - turn it back and forth - this might clean it and restore normal operation. * Power supply or connection to CRT neck board - insufficient voltage will result in the CRT never totally blanking. Check (usually scan derived) power supply components (from flyback). * General power supply - check B+ for correct value and ripple. A main power supply fault might result in these symptoms (and usually many others). * Blanking circuit - this may be a part of the video/chroma chip or separate. Check waveforms to determine if the blanking pulses are making it to the video output. Red, green, or blue retrace lines:--------------------------------- Where only one color is showing, suspect an incorrectly adjusted individualbackground/bias control or bad part on the CRT neck board for that color. * Individual brightness/background/bias control(s) - mark setting of pot for the problem color and then see if a slight adjustment removes the retrace lines. See the chapter: "TV Adjustments". Of course, if this happened suddenly, the problem is not due to a misadjusted control though a dirty pot is possible - turn it back and forth - this might clean it and restore normal operation. * Component or connection on CRT neck board - insufficient voltage to or incorrect biasing of the video driver for this color can result in the CRT never totally blanking. Compare voltages and signals, and swap components between good and bad channels to confirm. * Blanking circuit - this may be a part of the video/chroma chip or separate. Check and compare waveforms of good and bad colors to determine if the blanking pulses are making it to the video output. There is a slight possibility that a bad CRT may result in visible retracelines. To eliminate this possibility: * Disconnect the filament - all evidence of a picture, raster, and retrace lines should disappear once the filaments/cathodes have cooled (15 seconds or so. If there are still visible retrace lines, the CRT is suffering from cold or field emission from someplace (may not even be the cathode). * Turn down the screen (G2) control on the flyback (usually). If one color remains no matter how you set the control, again there is some kind of weird emission from the CRT. However, if white/gray retrace lines remain, the problem may be in the screen supply. See the section: "Bad CRT causing retrace lines". Bad CRT causing retrace lines:----------------------------- (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). The TV which I bought last started developing retrace lines after a month orso of use. I took it back to the lab for warranty (special deal) and had itexamined by the real experts. They found that even with the filament supplydisconnected and VG2 at 0V the screen would still light up. They could evensee that the electrons weren't even coming from the cathode. That was withonly the picture tube in a test rig. So in this case the obvious conclusionhad to be that the tube was bad, and it was replaced (32" 16:9 SF, very $$).It had something to do with processing problems during manufacturing of theelectron guns. So even if this was a rare case, it *can* happen that retrace lines are dueto a bad picture tube. It's more usual to suspect the VG2 (screen voltage)or a defect somewhere in the RGB video path. Red, green, or blue full on - fog over picture:---------------------------------------------- This could be a heater-cathode (H-K) short in the CRT or a failureof a component in the chroma circuits or video output (driver board). Don't panic - heater-cathode shorts in CRTs can often be worked around. Note: before proceeding, it is a good idea to make sure that the screen isdegaussed - else you could be attempting to track down problems with the wrongcolor! Some simple tests can confirm or rule out other possibilities. * Compare the voltages for the video drive signals to the CRT on the little board on the neck of the CRT with the CRT both connected and unplugged. A schematic will help greatly in locating these signals. - If there is a significant difference especially on the bad color, then the CRT is a likely candidate. Try tapping the neck of the CRT GENTLY (with it plugged in and while viewing a picture) to see if it is an intermittent problem. - If there is no significant difference, you may have a bad driver or a problem in the chroma circuits. * Look for bad connection/cold solder joints, probably on the little board on the neck of the CRT. Use an insulated stick to gently prod the board and its components in an effort to induce/cure the problem. Look carefully for hairline cracks around the component leads. * You can swap components between two colors and/or test with an ohmmeter on that driver board to determine what is bad. The nice thing about color monitors and TVs is that there three copies of each of these components. Swapping and/or comparisons between these is an excellent diagnostic technique. * Another simple test: Disconnect the cathode for the full-on color from its drive. If it is still full-on, there is probably an H-K short in the CRT since the only way to get each color on the screen is via the cathode connection to the CRT neck board. If it is removed and there is still that color, the current must be taking another path inside the CRT. * Alternatively, interchange the outputs of the bad color with a good one by jumpering on the video driver board (on the CRT neck). If the bad color changes, then the problem is in the circuitry and not the CRT. Here is the procedure in more detail (example for red full on): (From: J. K. Emerine (jkemerine@aol.com)). To identify if the fault is in the crt or a control problem try this (WITH SET OFF): On the CRT board, lift the output end of the green cathode final resistor. Do the same with the offending red cathode's resistor. Use short insulated jumpers to 'swap' drive signals - drive the red cathode with the green drive and the green cathode with red drive. (Note that if this problem only occurs after a warmup period, color at turn on will be - well - wierd, but it is just a test.) - If the symptom returns = 'goes red' the CRT is shorting. (See the section: "Providing isolation for a CRT H-K short". --- sam) - If instead the symptom becomes 'goes green' then the red drive leg has the fault and the CRT is probably good. (In this case, there may be bad connections or a bad component on the CRT drive board or further back in the chroma circuitry. --- sam) Shorts in a CRT:--------------- Occasionally, small conductive flakes or whiskers present since the day ofmanufacture manage to make their way into a location where they short outadjacent elements in the CRT electron guns. Symptoms may be intermittent oronly show up when the TV or monitor is cold or warm or in-between. Somepossible locations are listed below: * Heater to cathode (H-K). The cathode for the affected gun will be pulled to the heater (filament) bias voltage - most often 0 V (signal ground). In this case, one color will be full on with retrace lines. Where the heater is biased at some other voltage, other symptoms are possible like reduced brightness and/or contrast for that color. This is probably the most common location for a short to occur. * Cathode to control grid (K-G1). Since the G1 electrodes for all the guns are connected together, this will affect not only the color of the guilty cathode but the others as well. The result may be a very bright overloaded *negative* picture with little, none, or messed up colors. * Control grid to screen (G1-G2). Depending on circuitry can result in any degree of washed out or dark picture. * Screen to focus (G2-F). Screen (G2) and focus voltage will be the same and the controls on the flyback will interact. Result will be a fuzzy white raster with retrace lines and little or very low contrast picture. Symptoms will be similar to those of a flyback with breakdown in the focus/screen divider network. * Focus to high voltage (F-HV). High voltage will be pulled down - probably arcing at the focus spark gaps/other protective devices. Line fuse and/or HOT may blow. A high impedance short may only result in increased focus voltage but this is probably unusual. * Other locations between electron gun elements as feed wires. Replacing the CRT may be required but there are a variety of 'techniques' thatcan often be used to salvage a TV that would otherwise end up in the dumpsince replacing a CRT is rarely cost effective: 1. Isolation - this will usually work for H-K shorts as long as only one gun is involved. 2. Blowing out the short with a capacitor - depending on what is causing the short, this may be successful but will require some experimentation. 3. Placing the CRT (TV or monitor) face down on a soft blanket and *gently* tapping the neck to dislodge the contamination. Depending on the location of the short, one side or the other might be better as well. Sometimes, this can be done in-place while watching the picture. A combination of (2) and (3) may be required for intermittent shorts whichdon't appear until under power. See the sections below for additionaldetails. However, for shorts involving the focus and high voltage elements,even a sharp edge can result in arcing even if there is no actual short.There is no remedy for these types of faults. Providing isolation for a CRT H-K short:--------------------------------------- This procedure will substitute a winding of your own for the one that isbuilt in to the flyback to isolate the shorted filament from the groundor voltage reference. Note that if you have a schematic and can determinewhere to disconnect the ground or voltage reference connection to thefilament winding, try this instead. The flyback is the thing with the fat red wire coming out of it (and perhapsa couple of others going to the CRT board or it is near this componentif your set has a separate tripler) and may have a couple of controls forfocus and screen. It should have some exposed parts with a ferrite coreabout 1/2-3/4" diameter. The filament of the CRT is the internal heater for each gun - it is whatglows orange when the set is on. What has happened is that a part of thefine wire of the bad color's filament (assuming this is indeed your problem)has shorted to the cathode - the part that actually emits the electrons.Normally, the heater circuit is grounded or tied to a reference voltageso when it shorts to the cathode, the cathode voltage level is pulled toground or this reference. You will need some well insulated wire, fairly thick (say #18-22). Find aspot on the flyback where you can stick this around the core. Wrap twoturns around the core and solder to the CRT filament pins after cutting theconnections to the original filament source (scribe the traces on the boardto break them). Make sure you do not accidentally disconnect anything else. This winding should cause the filaments to glow about the same brightness asbefore but now isolated from ground. If they are too dim, put another turnon the flyback to boost the voltage as this will result in low emission,blooming, and possible damage to the cathodes after awhile. (Don't gooverboard as you may blow the filament totally if you put too many turns onthe core - you then toss the TV.) Route the wires so that there is no chance of them getting near the highvoltage or any sharp metal edges etc. Your picture quality may be a tadlower than it was before because of the added stray capacitance of thefilament wiring being attached to the the (formerly bad) video signal, buthey, something is better than nothing. If you are not inclined to build your own isolation transformers, kits areavailable: (From: Alan Harriman (capstv@sprynet.com)). A company called KDTV/IWE carries kits (core, wire and tie) for $3.30 each.It takes all of two minutes to wind. Check out: http://www.seidata.com/~kdtv. BTW, I am just a satisfied customer. Rescuing a shorted CRT:---------------------- If the short is filament-cathode (H-K), you don't want to use the followingapproach since you may blow out the filament in the process. If this is thecase, you may be able to float the filament and live with the short (see thesection on: "Red, green, or blue full on - fog over picture". Shorts in the CRT that are between directly accessible electrodes canbe dealt with in a more direct way than for H-K shorts. At this pointyou have nothing to loose. A shorted CRT is not real useful. If the short is between two directly accessible electrodes like cathode-grid,then as a last resort, you might try zapping it with a charged capacitor.Start with a relatively small capacitor - say a few uF at a couple hundredvolts. Check to see if the short is blown after each zap - few may be needed.Increase the capacitance if you fell lucky but have had little success withthe small capacitor. If the fault is intermittent, you will, of course, need to catch the CRTwith the socket disconnected and the short still present. Try some gentletapping if necessary. If you do this with the charged capacitor acrossthe suspect electrode, you **will** know when the short occurs! Picture tube replacement:------------------------ It is possible to replace the picture tube. However, this is likely tobe both expensive and possibly time consuming with respect to adjustmentslike purity and convergence. When replacing: * Discharge both the old and new tubes before you start to be sure you won't have any unpleasant surprises. * Take extreme care when handling - at the very least, a slip can result in a broken neck and a bad and expensive day. "The 25VCXP22 picture tube of my RCA Accutouch XL-100 CCU-942 TV start fading. Its 100% transistorized, everything still works perfectly after about 20 years service. but: * Can I still buy new RCA 25VCXP22 picture tube? What is the approximate cost? * Any equivalent tube for direct replacement? Cost? * If no replacement picture tube is available, what is other option?" (From: Chris Jardine (cjardine@wctc.net)). What you have here is genericly referred to as the 25V as opposed to the 25Apicture tube. While there are minor differences with respect to the lettersafter the V for the most part they are interchangeable. When I worked my waythrough engineering college I worked at a TV repair shop and my job was mostlychanging picture tubes. Yeah, we did enough of them to keep a tech busy 4 to 5hours a day changing them and I got pretty good and could change, colorbalance, convergence, etc. the tube in about 45 minutes. We for the most partused 3 major tubes, 1) 25A, 2) 25V, and 3) 21FJ (a little nostalgic for thosewho remember this one). This was back when your TV would have been fairly new(1981 to 82). These are available from many different sources - RCA, ChannelMaster, Wisconsin Tube, etc. The price would vary depending on the quality ofthe tube. I remember that we could get a 25A for about $35 at the time due toour volume - one truck per month. The most expensive I've seen them has beenjust over $200. This is quite a range and there are now many other types oftubes including in-line, trinitron, etc. I hope this helps and thanks for the trip down memory lane! (From: Chris Jardine (cjardine@wctc.net)). The important thing here is that the tube begins with 25V. If it does it shouldwork in your set. The only thing you have to know is whether the tube has'ears' attached permanently. The 25V comes both with and without these mountingears permanently attached. I know that you can still get one of these from anyof a number of suppliers. I know that Channel Master and RCA (Thompson,whatever!) still make them available as well as any of a number of local CRTrebuilders. Dark picture:------------ A TV or monitor with a picture that is too dark may have a fault or the CRT mayjust be near the end of its useful life. First, confirm that your video source - computer, camera, etc. - is producinga proper signal. Is the brightness at all erratic? Does whacking the monitor have any effect?If so, then you may have bad connections on the CRT driver card or elsewhere.If the brightness tends to fade in and out over a 10 to 20 second period,a bad filament connection is likely. Check for the normal orange glow ofthe filaments in the neck of the CRT. There should be 3 orange glows. Ifthey are excessively reddish, very dim, or fade in and out, you have locateda problem. See the section: "Picture fades in and out". Common causes of brightness problems: 0. Dirty CRT faceplate or safety glass. Don't laugh. It sounds obvious, but have you tried cleaning the screen with suitable screen cleaner? It is amazing how dirty screens can get after a few years - especially around smokers! Wipe gently with a slightly dampened cloth - not soaking or you may end up with real problems when the water drips down inside and hits the electronics! On TVs with a separate protective faceplate, clean both the front and rear surfaces of this plate as well as the CRT itself. 1. Old CRT. The brightness of the CRT deteriorates with on-time. It does not matter much how bright your run your TV. An indication of a weak CRT would be that turning up the SCREEN (G2) or master brightness control only results in a not terribly bright gray raster before the retrace lines show up. There may be indications of poor focus and silvery highlights as well. A CRT brightener may help. See the section: "Brightening an old CRT". 2. Bad component in filament circuit or bad connection reducing filament voltage. This should be easy to check - there are only a few parts involved. If it is erratic, bad connections are likely. 3. Brightness control faulty - bad pot, bad connections, or problem with its power supply. Depending on specific problem, control may or may not have any effect. If digitally adjusted, there could be a problem with the logic or control chip. If the button or menu item has no effect at all, then a logic or control problem is likely. 4. Improperly set SCREEN (G2) voltage (usually on flyback) or faulty divider network. See the section: "Adjustment of the internal SCREEN and color controls". 5. Improperly set video bias (background) levels or fault in video drive circuitry. See the sections starting with: "Optimal procedure for setting brightness/background and screen adjustments". 6. Fault in video amplifiers. With all three color affected equally, this would most likely be a power supply problem. A video amplifier problem is likely if turning up the SCREEN (G2) or master brightenss control results in a very bright raster before the retrace lines appear. Cheack signals out of the video/chroma(IC. 7. Fault in beam or brightness limiter. Many TVs and monitors measure the beam current (possibly indirectly) and limit the maximum to a safe value. The purpose of this may be to protect the CRT phosphors, and/or to assure that the power supply does not go out of regulation, and/or to limit X-ray emission. If this circuit screws up, a dark picture may result. Checking the signals and voltages at the CRT socket should determine if this is the problem. 8. High voltage is low. However, this would likely result in other symptoms as well with focus, size, and geometry. Brightening an old CRT:---------------------- If performing adjustments of the internal background and/or screen controlsstill results in a dark picture even after a long warmup period, the CRTmay simply be near the end of its useful life. In the old days of TVswith short lived CRTs, the CRT brightener was a common item (sold in everycorner drugstore, it seemed!). You can try a similar approach. Caution: this may shorten the life ofthe CRT - possibly quite dramatically (like it will blow in a couple ofseconds or minutes). However, if the monitor or TV is otherwise destinedfor the scrap heap, it is worth a try. The approach is simple: you are going to increase the voltage to thefilaments of the electron guns making them run hotter. Hopefully, justhotter enough to increase the brightness without blowing them out. Voltage for the CRT filament is usually obtained from a couple of turnson the flyback transformer. It is usually easy to add an extra turn or twowhich will increase the voltage and thus the current making the filamentsrun hotter. This will also shorten the CRT life - perhaps rather drastically.However, if the TV or monitor was headed for the dumpster anyhow, you havenothing to lose. Picture tube brightener:----------------------- (From: Kevin Carney (carneyke@mhv.net)). Try a CRT brightener from MCM Electronics about $20. It boosts thefilament voltage a volt or two. I have used them before and they help.You can also try running a power supply on the filament with themonitor OFF. Set the supply at the filament voltage and slowly bringthe voltage up. If the filament is 6.3 volt bring it up gradually to10 -12 volts for about a half hour. This will brighten it up some.Be careful because too much voltage can open the filament ! Before doing this did you check the screen voltage setting and theRGB settings for drive and background ? There are also commercial CRT rejuvenators that supposedly zap thecathodes of the electron guns. A TV repair shop may be able toprovide this service, though it is, at best, a short term fix. More drastic measures to brighten CRT:------------------------------------- (From: LEE (leep@mailhub.scf.lmsc.lockheed.com)). As a start, I crank the brightness control all of the way up. I then turn thecolor control all of the way up. I let the set run with a bright screen foraround 15 min. This procedure cleans up the cathode surfaces so that they canemit more electrons. Now turn the controls back to normal and see if any improvement took place. If not, Wrap 2 or 3 turns of around 18 gauge insulatedwire around the flyback and add this extra power in series with existingfilament leads from flyback. You can experiment with the number of turns etc.to get brighter filaments. do not run the filaments white - just a brightenedyellow. This will probably turn out to be around 8-9v in most cases. I had todo this on two different Sanyo replacement flybacks as they had low filamentvoltage from the factory. (flakey replacement parts). I`ve been running one ofthese Sanyos for around 4 years now with a nice bright picture (13") Left portion of screen is dark or faded:--------------------------------------- "I've got an old TV where the left 1/3 of the screen is 'faded'. It is especially noticable when a dark picture is showing (like a night time scene)." This is normally caused by a bad filter capacitor on the power supply line(typically 200 V) that feeds the RGB output transistors. It is usually a scanderived voltage off of the flyback. Look for an electrolytic capacitor ofaround 4.7 to 10 uF, 160 to 250 V fed from a rectifier diode on this supply. Color balance changes across screen from left to right:------------------------------------------------------ The characteristics are that a solid white screen will tend to be blue tintedon one side and red tinted on the other. This is usually a subtle effect andmay be unavoidable with some designs. There are several possibilities: 1. Purity - this means the beams are landing on the wrong phosphor dots. This is what would be affected by moving from one location to another or even rotating the TV on its base without degaussing. If the problem just appeared, degaussing may be needed. What do you have near the TV or monitor? Loudspeakers or other devices which generate magnetic fields can easily cause all sorts of color purity problems. Relocate the offending device(s) or the TV or monitor and then degauss it. See the section: "Degaussing (demagnetizing) a CRT". If the problem still persists, purity adjustment may be needed. However, this isn't likely to have changed so look for other causes before tackling these adjustments. 2. Unequal electron gun to shadowmask/screen distance - the electron beams for the red and blue video travel slightly different distances on the left and right sides of the screen so their intensity (due to focus not being optimal and other factors) in each case may differ slightly affecting color balance. 3. Doming - This would only happen in very bright areas and causes the shadow mask to expand and distort. (Doming should not be a problem with Trinitron CRTs which use tensioned wires in their aperture grill.) This would also not really affect left-right color balance in particular. I don't really know how much of a problem (2) is in practice or whether somemanufacturers compensate for it. Bleeding highlights:------------------- On very bright areas of the picture, one or more colors may bleed tothe right resulting in a trail of those colors. The difference betweenthis problem and the section: "Trailing lines in one or more colors" isthat in this case, only highlights are affected. One cause of this is that the color gain, contrast, or intensity controls(whatever they are called on your set) are set too high. See the sectionon: "Color balance adjustment". Check the settings of any brightness limitercontrols as well. Trailing lines in one or more colors:------------------------------------ Assuming this is not a form of ghosting resulting from poor receptionconditions, then it could be any of the following: * Poor decoupling in the power supplies for the video drive circuits - probably on the CRT neck board. Check for bad (low uF or high ESR) filter capacitors (electrolytic mostly) on this board or the power supplies feeding it. * Insufficient CRT filament voltage. This could be a result of bad connections or a bad component in the filament power supply (probably from the flyback). Check to see if the filaments are glowing bright orange and check the voltage if possible (though this can be tricky since it is often fed from a winding on the flyback and is a pulse waveform, not DC or a sinusoid. The service manual (or Sams' Photofact) will probably have info and waveforms. * Bad CRT (more likely if only one color is affected). A weak electron gun can result in this behavior. Swap it with one that work properly. If the same color is still bad, that CRT gun is weak. The CRT will need rejuvenation or need to be replaced (more likely, the entire TV will be tossed into the dumpster). Brightness changes from left-to-right across screen:--------------------------------------------------- Slight variations in brightness across the face of the CRT are not unusual.In fact, if you used a photometer to actually measure the brightness, youmight be amazed at the actual variance even with the best TV - you justdon't notice it. However, a major variation - usually a decay from left toright but could be the other way indicate a component failure. Of course,make sure the face of the screen is clean! * A fault in the power supplies to the video amplifier and/or video output circuits. Most likely, an electrolytic capacitor has dried up and is not adequately filtering the power derived from the flyback which then has ripple at the horizontal scan rate and thus locked to the screen. The voltage decays from left-to-right between horizontal flyback pulses. The most likely location for these capacitors is in the vicinity of the flyback transformer on the mainboard or on the CRT neck board. Check the capacitors with capacitor tester or ESR meter and/or take a look at the power right at the video amplifier and video output drivers. * Horizontal linearity is bad - this may actually be a horizontal geometry problem and not a brightness problem. See if objects on left side of the screen are stretched compared to those on the right (or vice-versa). If they are, the problem is in the horizontal deflection circuits - possibly a bad S correction capacitor or linearity coil. * Inoperative degauss circuit, TV moved or rotated without degaussing, or magnetic field from some other device (like a permanent magnet) is affecting CRT - slight amounts of magnetization may reduce brightness (by moving the beams into the black space between phosphor dots) before affecting color purity (where the beams land on the wrong phosphor dots). Try deguassing manually. See the section: "Degaussing (demagnetizing) a CRT". Picture fades in and out:------------------------ If the picture faded away on the order of 10-20 seconds (and if it comesback, also comes up to full brightness in same time frame - possiblywith the persuasion of some careful whacking) AND with NO othersignificant changes such as size, focus, etc., then take a look in the back ofthe tube for the filament to be lit - the orange glow near the CRT socket. Ifthere is none, then you probably have a bad solder connection on the circuitboard on the neck of the CRT. Look for fine cracks around pins on that board.Try prodding it with an insulating stick to see if the picture comes back.Resolder if necessary. It is probably not a bad CRT as the filamentsare usually wired in parallel and all would not go bad at the same time. However, if only a single color fades in and out, then a bad connectioninside the CRT is a distinct possibility - look for only one of thefilament's glow to be coming and going. This is probably not worth fixing. If the picture faded away with other symptoms, then there is probablya fault in the video amplifier/output one of its power supplies -still probably a loose connection if you are able to get it back bywhacking. Occasional brightness flashes:----------------------------- These may last only a fraction of a scan line or much much longer. This could mean an intermittent fault in a variety of places includingthe video circuitry and SCREEN power supply: * Brightness circuitry - SCREEN, master background or its power supply. Could be in or around flyback or focus/screen divider. Could perhaps be in the CRT, but probably less likely. * Video amp before or at chroma demodulator - since after this point, you would most likely get colored flashes since only one of the RGB signals would likely be effected. If you get it from all sources, then tuner/IF is ruled out. Suppose you just have no signal to a direct video input. What do youget? If you still get flashes, it should be real easy to monitor eitherthe video outputs or SCREEN supply (with a HV divider on your scope) fornoise. Then trace back to power or noise source. Excessive brightness and/or washed out picture:---------------------------------------------- There are a number of possibilities including incorrect screen (G2) or bias(G1) voltages, or a problem in the video or blanking circuitry. Any of thesecould be the result of bad connections as well. A short in the CRT can alsoresult in these symptoms. * Excessive brightness/washed out picture is often an indication of a problem with the screen (G2) supply to the CRT. May be a bad capacitor or resistor divider often in the flyback transformer assembly or on the board on the neck of the CRT. * If the excessive brightness just developed over time, then a simple adjustment of the screen or background brightness controls may keep it (and you) happy for a long time. When good, a typical value would be in the 200 to 600 VDC at the CRT. The screen (it may also be called master brightness, bias, or background) control should vary this voltage. However, it may be difficult to measure as the resistors in the voltage divider network may be quite large - hundreds of M ohms. If your unit has an external screen control (less likely these days) and it has no effect, trace out the circuitry in the immediate vicinity and check the resistors and potentiometer for opens, look for bad connections, etc. If it is built into the flyback transformer and is sealed, the entire flyback will need to be replaced unless the actual problem turns out to be a bad connection or bad component external to the flyback. * Where the brightness control has no effect, suspect a missing bias supply to the G1 (control grid) electrodes of the CRT. This is usually derived from the flyback with a simple rectifier/filter capacitor power supply. Parts may have failed (though not likely the flyback itself). Adjusting the user brightness control should vary this voltage over a typical range of 0 to -50 V with respect to signal ground. * It could also be a problem with biasing of the video output transistors. There may individual controls for background brightness on the little board on the neck of the CRT. However, we are looking for a common problem since all colors are wrong in the same way. This is likely to be a missing voltage from a secondary supply from the flyback. * A short between electrodes inside the CRT can result in brightness problems. It may be possible to check this with an ohmmeter with the power off and the CRT socket removed. Test between G1, G2, and F where all colors are affected though a short between F and G2 will result in the focus control changing brightness and vice-versa - a classic symptom. However, in some cases, it only shows up when operating and one must deduce the presense and location of the short from its affect on voltages and bias levels. See the section: "Rescuing a shorted CRT" and other related topics. First, check for bad connections/cold solder joints by gently proddingwith an insulating stick. Check voltages and bias levels. Bad focus (fuzzy picture):------------------------- Focus voltage on the CRT is usually in the range of 2-8 KV DC and shouldbe controllable over a fairly wide range by the focus pot - usually locatedon the flyback or a little panel in its vicinity: * If adjusting the pot results in a position of acceptable focus, you may be done. It is not unusual for the focus setting to drift a over time. * If the setting is already as good as possible but not really good enough, the CRT may be tired. Alternatively, the filament voltage may be too low. Check for bad connections in the filament circuit. * If the optimal setting is out of range of the focus pot, the problem is likely leakage in the focus divider in the flyback or one of the components on the CRT neck board. Also see the sections: "Focus adjustment" and "Focus drifts with warmup". The focus wire usually comes from the flyback or if the general area or from aterminal on a voltage multiplier module in some cases. It is usually a wireby itself going to the little board on the neck of the CRT. If a sparkgap (a little 2 terminal device with a 1/8" gap in the middle)is arcing with power on, then the resistive divider has shorted insidethe flyback, focus board, or HV multiplier - whatever you TV has - andthe this unit will need to be replaced. Ditto if the SCREEN control affectsfocus and/or vice-versa. Using a suitable high voltage meter (range at least 10 KVDC, 1000 M ohm orgreater input impedance), you should be able to measure it connected anddisconnected. The ground return will be the outside coating of the CRT whichmay or may not be the same as the metal chassis parts. If the voltage is verylow (less than 2 KV) or too high and the pot has little effect: * When measured right off of the source disconnected from the CRT neck board, then the problem is probably in the focus network in the flyback (or wherever it originates). Sometimes these can be disassembled and cleaned or repaired but usually requires replacement of the entire flyback or voltage multiplier. Note: you may need to add a HV (10 KV) capacitor between the focus wire and DAG ground to provide filtering so you get a DC level for your meter. * When measured with the focus wire attached to the CRT neck board with the CRT connected but reasonable with the CRT unplugged, there is probably a short between the focus and another electrode inside the CRT. See the section: "Rescuing a shorted CRT". * When measured with the focus wire attached to the CRT neck board with the CRT unplugged, there is likely a component on the CRT neck board that is leaky or breaking down. Also, check for decayed (tan or brown) glue which may turn leaky with age. Focus drift with warmup:----------------------- This could be due to a problem with the focus voltage power supply, componentson the CRT neck board, or a tired worn CRT. Focus is controlled by a voltage of 2-8 KV DC usually derived from the flybacktransformer and includes some resistors and capacitors. One of these couldbe changing value as it warms up. (assuming nothing else changes significantlyas the unit warms up - e.g., the brightness does not decrease.) Focus voltage is derived from a subset of the high voltage winding on theflyback using a resistive voltage divider which includes the focus pot.These are extremely high value resistors - 200 M ohm is common - and soleakage of any kind can reduce or increase the focus voltage. All otherthings being ok - i.e., the picture is otherwise fine - I would suspect thistype of failure rather than the CRT. The connection to the CRT is usually a separate wire running from the flybackor its neighborhood to the CRT neck board. Look for components in thisgeneral area. Use cold spray or a heat gun to isolate the one that isdrifting. If you have access to a high voltage meter, you should be ableto see the voltage change as the TV or monitor warms up - and when you coolthe faulty part. If it is in the flyback, then sometimes the part with theadjustments clips off and can be repaired or cleaned. Most often, you willneed to replace the flyback as a unit. * If the optimal adjustment point of the focus control doesn't change that much but the best focus is simply not as good as it should be, the CRT is probably the problem. However, if the optimal point produces acceptable focus but it changes (and possibly moves off of one end of the adjustment knob range) as the unit warms up, the flyback or one of the components on the CRT neck board are likely drifting. * If you have a high voltage meter, you can measure the focus voltage to determine if it is being changed by the focus pot and if it is in the ball park (2-8 KV typical). Sometimes, the part of the flyback with the focus pot can be snapped off and cleaned or parts replaced but usually you need to replace the whole unit. There may a capacitor or two on the PCB on the neck of the CRT that could have increased leakage as well thus reducing the focus voltage. * To determine if the CRT is the problem, for sharp focus after the unit has warmed up. Power-off for an hour or so and carefully pull the CRT neck board off of the CRT. Then, power up the unit. Let it run long enough such that there would have been a detectable focus drift. Now, power-down, plug the CRT neck board back in, and power-up. Watch the image as it appears on the screen: - If the focus starts out fuzzy and sharpens up as the image appears and gradually becomes sharper as the CRT warms up the CRT is likely tired. The only catch here is that plugging the CRT neck board into the CRT results in an additional load on the flyback due to the picture beam current which heats it more as well. Thus, if the problem takes a few minutes to appear, keep the brightness turned down except to check the appearance of the picture from time to time. You can set the focus control for optimum when warmed up and just turn the TV on in well in advance of your favorite shows or add a user focus adjustment by drilling a hole in the plastic case for an *insulated* screwdriver or flyback focus knob extender :-). The CRT may continue to function for quite a while so this is not impending doom. - If the focus is relatively stable as the image appears and increases in brightness *and* is about as sharp as it would be with the TV warmed up, the problem is most likely in the flyback. However, also check for bad components or decayed (tan or brown) glue on the CRT neck board. A drifting flyback will need to be replaced as it will probably get worse and fail completely. Clean the surface of the circuit board and CRT socket in the vicinity of the focus and screen terminals and traces. Contamination or just dirt and grime can easily cause problems especially on humid days since the resistance of these circuits is extremely high (100s of M ohms). - If the focus is relatively stable as the image appears and increases in brightness *and* is similar to what it would be with the monitor cold, you have a very strange situation where some load on the high voltage power supply, perhaps, is causing a thermal problem. This would be rare. Bad focus and adjustment changes brightness:------------------------------------------- This is the classic symptom of a short between the focus and screensupplies - probably in focus/screen divider which is part of the flybackor tripler. If you have a high voltage meter, measuring the focus voltagewill show that (1) it is low and (2) it is affected by the SCREEN controlSimilarly, the SCREEN voltage will be affected by the FOCUS control (whichis what is changing the brightness. There is a slight possibility that this may be in the CRT as well. Measurethe FOCUS and SCREEN voltage with a high voltage meter. If they are identicalpull the plug on the CRT. If they are now their normal values, then ashorted CRT is a distinct possibility - see the section: "Rescuing ashorted CRT". Charlie's comments on focus problems:------------------------------------ (From: Charles Godard (cgodard@iamerica.net)). Most true focus problems that I have encountered (when the IHVT is ok) arerelated to leaks or resistance on the focus output. The diming of the screenwhen the focus pot is adjusted leads me to think in terms of a leaky socket.I'd remove the ground from the crt socket to the tube dag and see if itsparks. If so there may be a leak in the socket to ground. It could also beleaking to another pin, such as the screen grid. A rhetorical question: Whathappens to the screen voltage when the focus pot is adjusted? I have seen sockets that had no arching or other telltale signs, leak throughthe plastic housing to ground out the focus voltage. Look closely at the screen. If the blurring is in the form of small circles,then you have an open or hi-resistance focus electrode inside the tube. Thecircles may vary in visibility with brightness. If you still haven't found the problem, try to confirm that this is truly afocus problem. Remove the crt socket and observe the hi-voltage. If itclimbs more than about 1k, say all the way up to 25kv, then you may have abeam current problem rather than a focus problem. In that case re-check allcrt board voltages. If you have done all of the above and removing the socket makes no change inthe hi-voltage, then try to determine why the hi-voltage is low. Watch the screen as the brightness, contrast, or screen control are adjusted.See if you can observe any signs of blooming. When the IHVT doesn't provideenough current to satisfy the demands of the tube for current, the the picturetends to appear to expand like a balloon. i.e., bloom. This can be caused bynot enough drive to the IHVT. Carefully monitor the b+ to the horizontal drivestages to see that is is stable and correct. Blank picture, good channel tuning and sound:-------------------------------------------- Since the tuner and sound are ok, horizontal deflection which usuallygenerates power for most of the set is also working. Does 'blank picture' means a totally black screen with the brightness and contrast controls having no effect whatsoever? Or, is there is no picturebut there is a raster - light on the screen? The direction in whichtroubleshooting should proceed differ significantly depending the answer. Here are some questions: 1. As above, is there any light on the screen at any settings of the brightness and contrast controls, and/or when switching channels. Can you see any raster scanning lines? 2. Can you hear the high pitched (15735 Hz) of the horizontal deflection? 3. Looking in the back of the set, can you see the glow of the CRT filament? 4. Do you get that static on the front of the tube that would indicate that there is high voltage? Any cracking or other normal or abnormal sounds or smells? Possible causes of no raster: * No or low high voltage (low voltage, deflection, or high voltage power supply failure). * Fault with other voltages like G1 or screen (G2) to CRT. * Filament to CRT not getting powered. * Drive to CRT bad/shut off as a result of fault elsewhere. For example, failure of the vertical deflection may disable HV or blank the screem to protect the CRT from burn-in due to the very bright horizontal line that would result. With some sets, it is possible that the X-ray protection circuitry will blank the screen without affecting tuning or audio. Possible causes of no video (but a good raster): Problem in video IF, videoamplifiers, video output, cutoff due to other fault. It could be as simple as a bad connection - try gently prodding the boardswith an insulated stick while watching the screen. Check for loose connectorsand reseat all internal connectors. Purple blob - or worse:---------------------- Have you tried demagnetizing it? Try powering it off for a half hour, thenon. Repeat a couple of times. This should activate the internal degausser.See the section: "Degaussing (demagnetizing) a CRT". Is there any chance that someone waved a magnet hear the tube? Remove itand/or move any items like monster speakers away from the set. Was your kid experimenting with nuclear explosives - an EMP would magnetizethe CRT. Nearby lightning strikes may have a similar effect. If demagnetizing does not help, then it is possible that something shiftedon the CRT - there are a variety of little magnets that are stuck on at thetime of manufacture to adjust purity. There are also service adjustmentsbut it is unlikely (though not impossible) that these would have shiftedsuddenly. This may be a task for a service shop but you can try yourhand at it if you get the Sams' Photofact or service manual - don't attemptpurity adjustments without one. If the set was dropped, then the internal shadow mask of the CRT may havebecome distorted or popped loose and you now have a hundred pound paperweight. If the discoloration is slight, some carefully placed 'refrigerator'magnets around the periphery of the tube might help. See the section:"Magnet fix for purity problems - if duct tape works, use it!" It is even possible that this is a 'feature' complements of the manufacturer.If certain components like transformers and loudspeakers are of inferiordesign and/or are located too close to the CRT, they could have an effecton purity. Even if you did not notice the problem when the set was new,it might always have been marginal and now a discoloration is visible dueto slight changes or movement of components over time. Color rings - bullseye pattern:------------------------------ This probably means the degaussing circuitry is terminating suddenly insteadof gradually as it should. The most likely cause is a bad solder connectionto the degauss thermistor or posistor or something feeding it. You can confirm this by manually degaussing the screen with the TV or monitorturned on. If the problem disappears, the above diagnosis is probably valid.Check for bad solder connections in the vicinity of the degauss componentsand AC line input. Magnet fix for purity problems - if duct tape works, use it!:------------------------------------------------------------ The approach below will work for slight discoloration that cannot be eliminatedthrough degaussing. However, following the procedures in the section: "CRTPurity adjustment" would be the preferred solution. On the other hand, themagnets may be quick and easy. And, where CRT has suffered internal distortionor dislocation of the shadowmask, adjustments may not be enough. In any case, first, relocate those megablaster loudspeakers and that MRIscanner with the superconducting magnets. The addition of some moderate strength magnets carefully placed to reduce oreliminate purity problems due to a distorted or dislocated shadowmask may beenough to make the TV usable - if not perfect. The type of magnets you wantare sold as 'refrigerator magnets' and the like for sticking up notes on steelsurfaces. These will be made of ferrite material (without any steel) and willbe disks, rectangles, flexible strips. Experiment with placement usingmasking tape to hold them in place temporarily. Degauss periodically toevaluate the status of your efforts. Then, make the 'repair' permanent usingduct tape or silicone sealer or other household adhesive. Depending on the severity of the purity problem, you may need quite a fewmagnets! However, don't get carried away and use BIG speaker or magnetronmagnets - you will make the problems worse. Also note that unless the magnets are placed near the front of the CRT, verysignificant geometric distortion of the picture will occur - which may be acure worse than the disease. WARNING: Don't get carried away while positioning the magnets - you will benear some pretty nasty voltages! (From: Mr. Caldwell (jcaldwel@iquest.net)). I ended up with the old 'stuck on a desert island trick': I duck taped 2 Radio Shack magnets on the case, in such a wayas to pull the beam back.!!!! A $2 solution to a $200 problem. My friend is happy as heck. RCA sells magnets to correct corner convergence, they are shaped like chevrons and you stick them in the 'right' spot on the rear of the CRT. (From: Tom Sedlemyer (wesvid@gte.net)). First set purity as best you can. Obtain some pieces of refrigerator door magnet strips from an appliancerepair shop (they usually have some lying around). Cut the strips into 1 inch pieces. Place a strip as on the bell of thepicture tube as close to the yoke as possible and in line with the corner thathas the purity error. Rotate the magnet until you correct the purity errorand tape it in place. Multiple magnet strips can be used and you mayexperiment with the size of the strips for best effect. It is very importantthat the strips are positioned close to the yoke or the effect will not hold.The only drawback to this method is some very slight distortion of thegeometry of the raster, but it beats hell out of paying for a new CRT. Color TV only displays one color:-------------------------------- I assume that now you have no other colors at all - no picture and noraster. Let us say it is red - R. It is probably not the CRT. Do you have a scope? Check for the R, G,and B video signals at the CRT. You will probably find no signalsfor the defective colors. This is almost certainly a chroma circuit problem as any failure of theCRT or a video driver would cause it to lose a single color - the othertwo would be ok. Therefore, it is probably NOT the CRT or a driver onthe little board on the neck of the CRT. Try turning up the SCREEN control to see if you can get a G and B rasterjust to confirm that the CRT is ok. Locate the video drive from the mainboard for the good and a bad color.Interchange them and see if the problem moves. If so, then there isa video signal problem. If not, it is on the little CRT board. It could be a defective chroma IC or something else in the chroma decoder. Disappearing Red (or other color):--------------------------------- Problem: I have been given an old colour TV. The reception is good, but veryoften, when the contrast and brightness of the TV image is low (e.g. whena night scene is shown), the red colour slowly disappears, leaving behindthe green and blue image and many red lines. The remaining red retrace are the giveaway that this is most likely nota CRT problem. (If there were no red lines, it could be the filament for the red gunof the CRT going on and off due to a bad connection inside the CRT - badnews.) How is a black and white picture? (Turn down the color control). If B/W picture is good, then the problem is somewhere back in the chromadecoder circuitry. Check the video input to the CRT video driver board and signals on that board.If B/W picture is also bad, then you can compare red and green signalsto determine where they are becoming different. The red lines in yourdescription sounds like the red video output circuit is drifting and messingup the background level, blanking, screen, or other setting. Could be acapacitor or other component. The wandering black blob on old Sony:------------------------------------ "I had a Sony KV1920 TV (very old) that suddenly started to displayed a black blob on the screen. The blob was anywhere from 1" around to almost the size of the entire screen. It had a sharp, not fuzzy, outline, and it would shrink in size as the TV warmed up, usually disappearing completely in 30 minutes. It shrank in sudden jumps, not gradually. Sometimes the blob would be stationary, other times it would tumble around rapidly all over the screen." (From: Raymond Carlsen (rrcc@u.washington.edu)). Measure the regulated +130 volt line... I think you'll find it has driftedupwards just enough to trigger the "protective" blanking circuit. In thosesets, if the B+ (and consequently the HV) went up, the screen wasautomatically blanked so you couldn't use the set. It was before HVshutdown. Older RCA TV sets used to throw the horizontal out of sync. Thelow voltage regulator is an analog type with a pass transistor that isprobably leaky, causing the high B+. Changes in line voltage and loading(with brightness changes) cause the partially blanked picture to change(the black blob moves around, sometimes blanking the entire screen). Whenyou replace the defective component, reset the 130 volts with the pot, andyou're back in business. The pot itself may have a bad spot... just move itone way or the other to get off that spot. Vertical brightness or color bars:--------------------------------- These are typically more or less equally spaced possibly more evident atthe left side of the screen. They result only in brightness or colorvariations, not deflection speed. Diagonal lines are straight and notsquiggly. Note that the appearance of these bars differs from those caused by ringingin the deflection circuits where diagonal lines will show a squigglingstair-step appearance. The most likely cause is a dried up electrolytic capacitor in the scan derivedpower supply for the video or chroma circuits or video output. Check for thisripple with a scope or test/replace any suspect capacitors. ****************** Tuner, AGC, and Sync Problems ****************** No reception from antenna or cable:---------------------------------- Make sure your source is providing a signal and that the cable connectorsare good (center pin not broken or bent). Try another TV if possible. Make sure you source select switch or mode is set correctly. Someonemay have accidentally set it to direct video or AUX input. Are all bands affected? If so, the tuner or IF is faulty. If there isa lot of snow, then it is probably toward the front (circuitry wise) ofthe tuner. If it is just a black screen, then it could be in the IF orvideo amplifier. If only certain bands are bad - channels 2-6 for example, then certainparts of the tuner circuitry are faulty. However, make sure the CATVmode is set correctly as this affects reception on a band-by-band basis. The problems may be due to bad solder connections of the tuner shields,connectors, coils, and other components. Try prodding the tuner to seeif you can make the problem come and go or at least change. Picture is overloaded, washed out, or noisy:------------------------------------------- This indicates an Automatic Gain Control (AGC) problem often caused bya dried up capacitor. You will probably need a schematic to go muchfurther. This could be a problem in the tuner, IF, or video amplifiers. The following assumes you are sure the signal source is strong - try a VCR orother local one (channel 3/4, not the RCA jacks). (From: Glenn Watkins (blueribb@mail.comcat.com)).Substitute a variable voltage source for the tuner's AGC voltage. Most of thetime the range of AGC is from 1 to 7 volts. If you can get a decent snowfree picture with an external AGC source, then the tuner is probably OK. Jumping picture on white scenes:------------------------------- This could be an AGC problem if the picture appears overloaded. However, ifthe picture is normal except unstable, the sync separate is the place tolook: (From: Jack Schidt (jack@wintel.net)). White screens are a worst case video pattern for sync separators, and willcause an erratic shift in the vertical multivibrator trigger level unlessthe horizontal and video information is filtered out [integrated] prior todriving the vertical sync input of the processor IC. This will show up with a scope as high frequency noise going into thevertical sync input. Look for a small electrolytic [in fact, all of them], around 1-10 uF or sonear the deflection/sync processor IC. Often simply increasing the value ofthis cap will help. Interference when using VCR RF connection:----------------------------------------- (Some of these comments also apply to use of LaserDisc players, satellitereceivers, video games, or other sources with RF modulator (Channel 3/4)outputs). This may consist of patterns or lines in the picture. If this only happens on the antenna or cable, it may be a problemwith these sources or the tuner in the VCR rather than the TV.As a test, try the connecting the TV directly to the antenna or cable. If it only happens on cable, there may be a (temporary) problem withcable transmission - contact your cable company. If it happens on playback of good quality (commercial) recordings, thenit could be a compatibility problem between the VCR and TV. Make sure your patch cable connections are secure and that the cablesare not damaged - in particular that the center pin is intact. Try fine tuning if your TV has this capability. If this does nothelp, try switching the channel 3/4 selector on the VCR to the oppositeposition and try that channel, sometimes one will be better than the otherparticularly if one of these or an adjacent channel is active in your area. If you have RCA baseband video inputs on your TV, try this connection tothe VCR. These should work better in any case. Confirm that it is not actually a problem with the VCR - try another TVif possible. If you just changed your component placement, the VCR or TV may bepicking up interference from another component. Turn off everything butthe VCR and TV and see if that identifies the culprit. Move the TVaway from the VCR so see if they are interfering with each other - theTV may be introducing interference into the VCR. Occasionally, the particular patch cable or its length may affectreception quality - try another one. If none of this helps, you VCR's RF modulator may be bad or slightlyweak. Alternatively, the tuner in the TV may be faulty. If receptionis generally noisy on all sources, AGC or RF/IF alignment may needadjusting. However, not all tuners are created equal. Your TV maysimply be making the best of a marginal situation. A light dimmer on the same circuit as the TV may result in similarsymptoms. If you are tuning up your motorcycle (or automobile) in thesame room, this may be spark ignition interference. RF Interference on TV:--------------------- "I have interference lines on my TV - they are particularly heavy on 2, not so prominent on 9 - one TV is on Radio Shack Color Supreme 100 (souped up rabbit ears), other is on a roof top antenna, both have coax from antenna to TV. I have HAM operator two doors away. Is there an FAQ on interference - if so where. How do I need to describe the interference pattern in order to seek help. Thanks." The FCC has an online interference handbook, with color photos showing howdifferent types of interference affect a TV's picture: * http://www.fcc.gov/Bureaus/Compliance/WWW/tvibook.html (From: Andrew Mitchell (amitchell@sympatico.ca)). Probably the easiest solution is to visit your ham neighbor anddescribe your difficulty. Amateur radio operators are licensed byfederal governments (FCC) and are required as part of their examinationto demonstrate a knowledge of this type of interference. It may well bethat the ham is not the source of the problem and even if this is thecase I'm sure he or she will be of assistance. (From: Alan N. Alan, WDBJ-TV, KM4IG (alann@intrlink.com)). OK, as a HAM myself, I can understand this. Channel 2 is the lowest TV channel,right above the six meter band, 50-54 Mhz. Channel 9 is well into VHF above175 Mhz. It is possible that your neighbor operates 6 meters. I would talk to him. First, the chances are it is YOUR equipment, and hisis legal and meets FCC specs. But I would be willing to bet he will be verycooperative to help you solve your interference. The thing to do is talk to him, calmly, and tell him about your problem. Then,schedule a time where he can transmit his gear and see if your problem existsalong with his transmissions.. If it does, you can go from there. Many hamclubs have many engineers and radio and TV people in their memberships thatwill jump in and help you solve your problem. Again, he is probably legal,and consumer equipment is not known for it's RF resistance. Consumermanufacturers cut corners wherever they can. This includes filtering anddesign. Problems with ground loops and video hum bars:--------------------------------------------- "I am having a problem isolating where my ground loop problem is coming from. The symptoms I see are Bars on my TV which scroll up the screen. The problem is these bars come and go, and when they are present they vary in intensity. I have verified that the cable ground is connected to the earth ground on the outside of the house, but the problem still remains. This problem is also screwing up any attempts to do video electronics experimentation. I am really tired of seeing these bars and any help you could give would be appreciated." (From: Paul Grohe (grohe@galaxy.nsc.com)). 1. Do these bars show up on other TV's connected to the same cable? 2. Is your TV connected to anything else? A/V receiver? VCR? If so, unplug *all* the equipment and plug it in one-at-a-time until the hum appears. If you have an AV receiver in the system, try running a jumper wire from the incoming CATV ground at the TV to the receivers chassis ground (usually the "phono ground screw"). If you have any devices with un-polarized plugs, unplug them and rotate them 180 degrees, and plug them back in. 3. If you connect a temporary antenna and view "off-the-air" signals, are the bars still there? If you still cannot eliminate the hum, try building a simple "ground isolator"out of two 75-300 ohm baluns, as described in the link below: * http://www.hut.fi/Misc/Electronics/docs/groundloop/antenna_isolator_building.html Place it as close to the TV as possible. (From: Charles Godard (cgodard@iamerica.net)). This seems like a cable company problem, but you need to prove it to the cableguy before he will start climbing pole's and changing amps and couplerslooking for an intermittent amp. (And I don't blame him.) At the main cable line to the house and remove all couplers and put a singleline from the cable direct to the rf input on a single tv, then watch it for afew of days. If the problem re-occurs call the cable guy and show him whatyou have done and explain the problem again. Put yourself in the shoes of the cable guy. He comes into a house with VCR'sand all the gadgets we all have hooked up to our TV's with lines running allover the house, and can't get to the back of the TV to see what's there, andhe's not a TV repair guy anyway and nobody else in the neighborhood iscomplaining and this problem may happen when it rains but it may not. mmmhhh If it does not show up on the single TV, then the problem is probably yours.Add one device at a time until you find the trouble maker. Start with theyour Cable AMPLIFIER. (From: 4real (alan69@iname.com)). You eliminate all of the other junk attached between your main cable input toyour house and your TV to be sure it isn't the cause. You will definitely want to suspect a problem with the amplifier you haveinstalled. Especially if it is one of those cheap ones. Usually when thefilter capacitor in an amplifier goes bad it will cause the hum bars you aredescribing, and they can be intermittent. Another problem may be that youhave too much signal going into the amplifier. Amps are rated to handle acertain amount of input signal (measured in db) depending on the number ofchannels you wish to amplify, and the gain provided by the amp. If you try tofeed an amplifier with too much signal it will overdrive it and cause avenetian blind, or herringbone effect. It could also be possible that thecable company is supplying a signal with reverse tilt. That means more signalon the lower channels and less on the higher ones. The lower channels mightbe the ones overdriving the amplifier. The only way to tell for sure is tomeasure it with a signal level meter. (very expensive unless you happen to bein the business and have one handy) If this is the case (too much signal goingin) you probably don't need the amplifier to feed only 2 TVs. The last thing I can think of and the cable guy should have checked this: Theyuse 60 VAC on their main trunk lines to power their line amplifiers. The tapswhich feed the individual houses are supposed to prevent this ac from going tothe individual lines. Occasionally one of these devices fails or a line guyforgets to pull a fuse and hence the ac gets sent to your tv. It won'tnecessarily fry your tv but can cause problems. It may even damage the tvtuners that are connected to that feed. In most cases if you touch the centerconductor of the cable and a good ground you can feel the ac. It isn't enoughto hurt you but you will definitely know it's there. To be on the safe sideyou should test it with a volt meter. (From: Cliff R. (craeihl1@nycap.rr.com)). My guess would be your cable amplifier. The fact that you see TWO bars on yourscreen tells me that it's 120 Hz interference - the frequency caused by ailingfull wave power supplies used in these amps. Take the amp out of the line fora few days. If you don't have "snow" in the picture with it out, s...can it!If you find it was bad and can't live without it, you might try making sureall your internal cable, splitters, and connections are good quality & in goodshape. Radio Shack stuff......well, it stinks! You can purchase primosplitters & cable from your cable company and its not thatexpensive. Certainly cheaper than an amp (which you might not need if thecabling were up to snuff). You could also cry to the cable company for more signal into your house. Thismay or may not work but it's worth a shot. I would put an amp in line only as a LAST resort. Most of the inexpensiveamps sold are......cheap. They can easily cause more trouble than they cure.If you must, go with a primo unit from Blonder-Tongue or Jerrold. (From: Charles Hope (charles.hope@argonet.co.uk)). It sounds very like a problem that I had and solved. Cause: Modern tv sets antenna connector does not have true earth on thescreen but is at a potential of half mains supply. It is possible to drawabout 30 micro-amps from this. Hum bars are induced in the amplifier because there is a small resistance inthe earth path between output and input giving about 1 volt drop of thisstray mains signal. Worse when raining because the cable ground is betterthen. Solution: Either ground the antenna screen or fit a "braid breaker" in thescreen. Missing or noisy channel or block of channels:--------------------------------------------- If you are unable to receive certain channels or blocks of channels,this is a tuner problem - could be as simple as bad connections - oreven simpler:. First, check to see that the tuning mode is correct - TV, CATV, asthis is the most common cause of channels 'disappearing'. TV channels are assigned frequencies ranging from 72 to almost 800 MHzdepending on broadcast or cable channel assignment. To tune over such awide range requires splitting it up into various bands even if these arenot actually defined. If you have a varactor tuned set, then you alreadyknow about the Vl, Vh, and U bands which may use separate front-endcomponents. Even modern quartz PLL synthesized tuners need to allocatecircuitry depending on frequency range. Therefore, if a block channels isnot working, it could be due to a failure of some component related to thatfrequency range. Aside from looking for bad connections, resoldering theshields and connector pins, prodding, pressing, praying, etc. you will needa schematic to have any chance of finding such a fault. There is another slight possibility. Some TVs have a parental lockoutcapability (pre V-chip) to prevent kids or other unauthorized access toselected channels. The channel selections may have been accidentallyaltered. Check your user manual for instructions on programming thisfeature. Even on models without this option, the same internal circuitrycould be present but not normally accessible. A power surge or stray cosmicray could have put the set in a screwy mode. Unplugging power for a minute or probably a much longer time might possibly reset such an anomaly. Loss of Channel after Warmup:---------------------------- If there is a general loss of picture and sound but there is light on thescreen, then most likely the tuner or IF stage is pooping out. With both no sound and no picture but a raster and static, it is mostlikely a problem in the tuner, power to the tuner, or its controller(if non-knob type). If it recovers after being off for a while, then you need to try a coldspray in the tuner/controller to identify the component that is failing.Take appropriate safety precautions while working in there! If it stays broken, then most likely some component in the tuner, itscontroller, or its power supply as failed. There is a slight chance thatit could be a bad solder connection - I have seen these in the tuner modulesof RCAs on several occasions (and many other manufacturers - apparentlynot a solved manufacturing problem even after 40+ years! Channel tuning drifts as set warms up:------------------------------------- This may be a slight drift - like someone is messing with the fine tuningor such a substantial change in tuning frequency that the channels go byas though you are surfing. Possible causes depend on tuner type: 1. Quartz tuner (10 button direct access digital synthesizer) - For a slight drift, a component is probably changing value, possibly the crystal in the reference oscillator. For gross changes - flipping through channels - it is more likely to be a digital control problem - the microcontroller is misdirecting the synthesizer to change frequency. 2. Varactor tuner (buttons but not direct channel access) - If only a single pushbutton selection is the problem, the the varactor tuning diode for that button is probably changing capacitance. If all channels in a band (Vl, Vh, U) are having a problem, it is more likely to be a drifting D/A or faulty AFT (Automatic Fine Tuning) circuit or power supply. 3. Turret or switch tuner (Knobs) - A component like a capacitor is changing value. You will have to get in there with a heat gun or cold spray and track it downthe old fashioned way. At least, the problem is almost certainly localizedto the tuner box (and possibly the controller if applicable). As noted, gradual slight changes in tuning are likely due to frequencydetermining components drifting. Uncontrolled channel surfing is probably a logic problem. For thequartz tuner, this could still be marginal connections causing themicroprocessor to misdirect the synthesizer to change channels. For the latter case, particularly, the cause may still be bad connectionsresulting in loss of channel memory and/or erratic behavior. Noise in picture and sound due to bright scene:---------------------------------------------- When a bright scene comes, the screen flashes and there is a lotof noise in the sound. When a dark scene comes, there is no flash or noise. Changing channel does not help. The noise persists even when the sound is muted. (The following is from: Lattuca@Midwest.net (Sam Lattuca)) When the video detector level is adjusted too high, you will get noise in the sound while screen contains a lot of white information (i.e. letters) but won't when only dark scenes are present. The video level adjust is usually a small coil normally located near the IF section. Since your set is several years old, this wouldn't be uncommon. It can be adjusted while watching the picture and listening to the sound. Internal interference - switchmode power supplies and digital circuitry:----------------------------------------------------------------------- (From: Mr. Caldwell (jcaldwel@iquest.net)). On virtually all newer televisions and in particular Mitsubishi televisionsthere is a problem with interference being emitted by the switched mode powersupply. The common symptom of this 'fault' is snake like dotted 'S' lines on channels2-6. It doesn't matter if it's cable, antenna or satellite(channel 3/4), thissymptom can occur. The common cause of this interference being allowed into the tuner is cabling.The super cheap 'suitable for garbage tie' cable that comes with even the mostexpensive VCR's is the culprit in most cases. The second is a set of rabbitears the least common is an open or high resistance to ground connection(usually at a connector) on the incoming cable line. To fix this there is only one reliable solution. All cabling must be hand madeRG-6 cable. Make as follows: * Strip the outer sheath of the cable to expose the braid and *fold the braid* away from the end so that it covers the unstripped outer braid. * Strip the inner conductor to it's proper length. * Install a good quality RG-6 connector *over the folded* braid. * Crimp with the proper RG-6 attachment to the cable crimpers, don't use a set of pliers or other -crushing- device. If the cable company doesn't water proof the outside connectors, Radio Shacksells a 'sealing tape' just for this purpose. Most cable companies use self sealing 'o-ring' connectors. (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). There is also interference from internal microprocessors and digitaltext generators (on-screen display, close captioning, teletext).And with 100 Hz digital television there is a wealth of sources ... Using only high quality shielded cable as described above seems like reallygood advise, FWIW I'd like to second that. I wish that everyone would takeantenna cables as seriously as you. Generally, double-braided cable (using copper foil for second shield) andcoaxially constructed connectors are recommended. But I think that thehand-mountable F-type connectors (Radio Shack) would be equally good, thoughless robust, if mounted properly. As far as antennas go, a decent rooftop antenna should always be better thanwhatever rabbit ear construction you might think of. In this case, distancecounts too, the antenna WILL pick up interference. Those darn rabbit ears:---------------------- So you bought a high performance TV and a set of $20.00 rabbit ears and thereare lines on channels 2-6. Go buy a set of rabbit ears that has *only* a coaxconnector on the back, throw the cable supplied with it in the bin for 'twistties'. Also buy an inexpensive surge suppressor that has a cable protector,enough RG-6 cable and connectors for two cables. * Make one cable long enough to get the antenna away from the set (12ft) and the other to connect the antenna to the surge suppressor. * Connect the long cable to the set and the other end to the surge suppressor. * Find an outlet away from the set and plug the surge suppressor in (pick the most sane order for all of this.) * Connect the shorter cable to the surge suppressor and connect the other end to the antenna. You're done and if you thought carefully you would have put the antenna nearyour easy chair so you can adjust the picture or put the antenna where you'llget the best reception and prevent interference. The surge suppressor wasneeded to ground the other end of the coax so as not to make the outer shieldan antenna for the interference from the TV's power supply. This method canalso help allevate 'dead spots' when using rabbit ears. Herringbone lines in picture:---------------------------- (From: Isaac Bergen (isaac.bergen@sympatico.ca)). Could be interference. If the pattern slowly moves up the screen, the problem is from the 60 Hz power. A line of dots or thin lines usually means corona discharge (arcing) from a nearby power line (especially on humid days). Could also be from a bad filter capacitor in the TV's power supply. A "checkered" pattern could be from a digital type noise source like a computer, etc. If you move the TV to another room and the interference changes, that's probably it. EM or RFI hell?:--------------- "About a mile from my home there are four TV (channels 2, 4, 9 and 14) and several broadcast FM transmitters, all working with powers in the 100+ Kw ERP class. Radio reception is a nightmare, mostly (I think) because of IM products in overloaded front end stages. In most bands there are several regions at a spacing of about 100 Khz, each 30 to 40 Khz wide with a harsh buzz stronger than anything else." (From: Don Klipstein (don@Misty.com)). If the buzz is of a frequency like the power line frequency or aharmonic thereof, then the nearby transmitters may not be the culprit.Instead, nearby corona on a high voltage power line, a nearby neon sign,or a nearby light dimmer may be the offender. Although the noise fromthese is usually broad-band, the noise could get concentrated into bandsspaced 100 KHz apart if something resonant around 100 KHz is involved inthe noise production. I would try temporarily turning off all fluorescent lights, neon signs,lights with dimmers, etc. and asking your neighbors to do the same to seeif any of these is the offender. I have often found light dimmers to bemajor RF noise sources. Possibly, an RF noise filter for the AC power for your receiver may helpthings. If you isolate a single offending appliance, it may help to plugit into an RF noise filter. If you use any filters with either theoffending appliance or the receiver, try all combinations of plug reversalto see what works best. Both leads of any offending appliance may notequally spew noise, and both lines in the filter may not equally blocknoise. Both lines of the receiver's power cord may not equally bringnoise into the receiver, if this is the route the noise takes. ******************* Audio Problems ******************* Picture fine, no audio:---------------------- First check that any muting control is not activated. This might bea button on the remote or set itself. If you have a headphone jack, itmay have dirty contacts as plugging in a headphone usually mutesthe speaker. If the set is mono or only one channel of a stereo set is out, thencheck for bad connections to the loudspeaker. Test the loudspeaker bydisconnecting one of the wires (with the power off!) and measuring itsresistance with an ohmmeter (it should be less than 100 ohms - probablyless than 8 ohms). Or momentarily touch a 1.5 volt battery to the speakerterminals - you should get a click or pop from the speaker. Next, trace back from the speaker output terminals to the circuit boardand look for bad solder connections or a loose or dirty connector. If these tests do not reveal anything, you probably need a scope (oraudio signal tracer) and schematic. Or at least the part number off ofthe chip. Is the final amp a chip also or just a transistor? Have youtested the transistor? If there is little or no buzz from the speaker,that would indicate a problem fairly near the output. If the tuner/if werebad, I would expect some noise/humm pickup from the low level audio stages.Get the part number off of the chip. If it is in a socket, check thecontacts for corrosion or looseness. Weak or distorted audio:----------------------- Assuming you are not attempting to play it at ear shattering levels,this may be due to an alignment problem in the IF/audio demodulator,a bad audio IC or other circuitry, bad connection, or a defective speaker. If your TV has an earphone or audio line out jack, try this to see if itis clear. If so, then your problem is in the final audio amp or speaker(s). If only one channel of a stereo TV is affected, it is almost certainly theaudio amp or speaker for that channel. Interchange connection to the twospeakers temporarily and see if the problem moves. If the problem is at all intermittent - try gently whacking the TV - thenit is likely a bad connection - either a cold solder joint or a dirtyor tired IC socket. The audio amplifiers in newer TVs are almost always ICs and replacementsare usually readily available. If the IC is in a socket, remove the IC,clean the pins and socket contacts and reinstall it. Sometimes, the contactson old socket lose their springiness and do not provide solid connections.Such a socket will need to be replaced. If the set uses discrete transistors, it s also possible for one of theseto become noisy. If your TV is fairly old - 10 years or so - this may be an alignment problemrequiring tweaking of a coil in the sound IF. See your service manual.It may be possible to have similar problems with newer TVs but this isrelatively rare. Buzzing TV:---------- Do you actually mean buzz - low frequency as in 60 Hz? Or, do you really meanhigh pitched whine. If the latter, see the section: "High pitched whine orsqueal from TV with no other symptoms". Or, it may be a combination of botheffects. Is the buzz through the speaker or from the inside of the set? * If it is the speaker, then it is a problem with the audio circuitry. This could be a design issue - very common or an actual fault (if it wasn't there before). It could also be interference caused by fluorescent lights or appliances like vacuum cleaners with universal motors or body massagers with vibrator interrupters (which generate sparks). Where the source of the problem cannot be located or eliminated, consider using a (HiFi) VCR for the tuner with an external stereo amplifier and the disable the internal speaker. * There is a slight possibility that the AC power in your house has some harmonic content - the waveform is not sinusoidal. This might be the case if you try to run on the same circuit as an active dimmer or something else with thyristor control. Proximity to heavy industry could also cause this. Relocating the offending device to another branch circuit may help. You could also try a line conditioner (not just surge suppressor) which includes filtering. Or, use a HiFi VCR as your audio source (see above). Else, petition to have that metal foundry move out of the neighborhood :-). * However, a buzzing that only occurs when the picture has sharply defined text or graphics, may be an overload problem at the source - some TVs simply handle it better than others. If it is a fault in the TV, an adjustment to the tuner or IF may be needed. (From: Paul Weber (webpa@aol.com)). Not to disparage proponents of the evil demon theory, but the phenomenon is more commonly known as "sync buzz". It is caused by poor performance in the TV's audio circuitry. It can usually be fixed by (1) reducing the signal strength and/or (2) tweaking the sound IF coil. Unfortunately, some of the latest TV receivers have no sound IF coil to adjust. If your TV has a sound IF coil, it can be done by ear, if you don't care about sound quality. However,I'd recommend taking it so a competent shop and describing the symptoms. Use the term "sync buzz in the audio," and they'll know what you mean. Be advised that it can't be cured in some TVs due to poor design. * If it is from inside the set (and not from the speaker), it is in the deflection (probably vertical) or power supply. Either of these can vary in severity with picture content due to the differing current requirements based on brightness. It could be a power supply transformer, deflection yoke, or other magnetic component. Even ferrite beads have been caught buzzing when no one was looking :-). Any of these parts could vibrate if not anchored securely or as they loosen up with age. Some hot-melt glue, RTV silicone, or even a strategically wedged toothpick may help. A new part may or may not quiet it down - the replacement could be worse! See the section: "Reducing/eliminating yoke noise". * Some TVs are simply poorly designed. You cannot infer the severity of this annoyance from any specifications available to the consumer. It is strictly a design (e.g. cost) issue. The size of the TV is not a strong indicator of the severity of the problem but there will be some relationship as the power levels are higher for larger sets. The best you can do is audition various TVs very carefully to find one that you are satisfied with. BTW, when I got my new super-duper RCA Colortrak in 1980, it had a similarannoying buzz - even had a repair guy out who behaved as though this was tobe expected. I did get used to it and am not even aware of it today - andstill use that set. Additional comments: (From: Karen (kclark9835@aol.com)). Also for some audio buzz problems especially in the older units don't overlookthe possibility of a misaligned trap. or a touch-up of the sound discriminatormay prove helpful. (From: Alan (algba@ix.netcom.com)). If the buzz is coming from the speaker suspect a bad saw filter in the ifcircuit (very common). If it is coming from elsewhere in the set it could be the flyback transformer,line input choke, or most common on those sets - the deflection yoke. I haverepaired many of these yoke by using a wooden shim and some silicone rubber.In the collar of the yoke just ahead of the lock down clamp, there are somemetal strips under the plastic. These are magnet that are used for convergencecorrection at the top and bottom of the picture. If you disturb them too muchit will throw off the convergence. High pitched whine or squeal from TV with no other symptoms:----------------------------------------------------------- First, make sure it is not coming from the loudspeaker itself. If it is,then we are looking at an unusual electronic interference problem ratherthan simply mechanical vibration. If it is a new set and think the sounds will drive you insane, returning itfor a refund or replacement may be best alternative. However, you may getused to it in time. I don't know about returning a set to a store thatdoesn't take refunds (I won't even ask about that!). In most cases, this sound, while annoying, does not indicate an impendingfailure (at least not to the set - perhaps to your mental health) or signifyanything about the expected reliability of the set though this is not alwaysthe case. Intermittent or poor connections in the deflection or power supplysubsystems can also result in similar sounds. However, it is more likely thatsome part is just vibrating in response to a high frequency electric current. There are several parts inside the TV that can potentially make this noise.These include the horizontal flyback transformer, deflection yoke, othertransformers, even ferrite beads in the horizontal deflection circuits. Inaddition, transformers or chokes in the switching power supply if this isdistinct from the horizontal deflection circuitry. You have several options before resorting to a 12 pound hammer: * As much as you would like to dunk the TV in sound deadening insulation, this should be avoided as it will interfere with with proper cooling. However, the interior of the entertainment center cabinet can be lined with a non-flammable sound absorbing material, perhaps acoustic ceiling tiles. Hopefully, not a lot of sound energy is coming from the front of the set. * Move the TV out of a corner if that is where it is located - the corner will focus sound energy into the room. * Anything soft like carpeting, drapes, etc. will do a good job of absorbing sound energy in this band. Here is your justification for purchasing those antique Persian rugs you always wanted :-). If you are desperate and want to check the inside of the set: * Using appropriate safety precautions, you can try prodding the various suspect parts (flyback, deflection yoke, other transformers), even lowly ferrite beads, with an insulated tool such as a dry wooden stick. Listen through a cardboard tube to try to localizing the source. If the sounds changes, you know what part to go after. * Once you have located the guilty party, some careful repositioning, a strategically wedged wooden toothpick, or a dab of RTV silicone or hot-melt glue may keep it quiet. Where the yoke is the guilty party, see the section: "Reducing/eliminating yoke noise". * It is possible to coat the flyback transformer, but this is used mostly when there a loose core or windings and you are getting not only the 15,735 Hz horizontal (NTSC) but also various subharmonics of this. This is probably acceptable but may increase the temperature of the flyback. * A replacement flyback (or whatever part) may cure the problem unless it is a design flaw or manufacturing quality problem. However, the replacement part could be noisier. You really do not want to replace the yoke (aside from the cost) as convergence and other service adjustments would need to be performed. Other transformers can be replaced. Note that the deflection frequency - just over 15 KHz for NTSC and PAL - ison the border of audible for adults but will likely be loud to younger peoplepossibly to the point of being terribly annoying - or worse. If you areover 40 (men more so than women), you may not be able to hear the fundamentalat all (at least you can look forward to silence in the future!). So, evensending the TV back for repair may be hopeless if the technician cannothear what you are complaining about! BTW, if you have a really old tube type TV, the power tubes (damper andhorizontal output) can also whine but these sets are few and far betweenthese days :-). Reducing/eliminating yoke noise:------------------------------- (From: Terry DeWick (dewickt@esper.com)). Carefully look under vertical core next to plastic liner, on top and bottom isa plate called the astigmatism shunt, it has come loose. Work RTV, epoxy, orservice cement onto it to glue it down and noise should quit. (From: TVman (tvman@newwave.net)). I have fixed a total of 27 of these sets with noisy yokes by removing theyokes and using motor armature spray sealant. If you carefully mark the EXACT position of everything (yoke, purity magnets),and slide the yoke off the CRT, then once the yoke has been sealed with motorarmature spray sealant and has dried thoroughly, put the yoke back EXACTLYwhere it was, there should be no problems. The only thing I have had to do was set the purity on one set, but itwas off a little to begin with. Whining when off?:----------------- Many TVs actually run their switchmode power supplies even when off to powerthe standby stuff like the remote control receiver, real time clock or timer,and channel memory. Depending on the design of the regulator, the power supplymay be running at a low chopper frequency due to the light load. Some people,dogs, and rodents are then annoyed. It could also be an indication of afault like a bad capacitor or loosened transformer core if this symptom justdeveloped - your hearing isn't likely improving :-(. There is so much running nowadays in 'off' electronics! **************** Miscellaneous Problems **************** General erratic behavior:------------------------ You press VOLUME UP and the channel changes or a setup menu appears all byitself just at the climax of your mystery story. Before you break out the screwdriver (or 12 pound hammer), cover up theIR remote sensor. Some types of electronic ballasted fluorescent lightsmay confuse the remote control receiver. Someone or something may besitting on the remote hand unit or it may be defective and continuouslyissuing a bad command. Or, the kids across the street may have nothingbetter to do than to drive your TV (and you) nuts with their remote! There is also a slight chance power line interference (from a light dimmeror external sources) may result in similar symptoms. See the section: "Wiringtransmitted interference". Assuming this is not the source of the problem: Check for bad connections - see if gently whacking the TV makes anydifference or triggers the errant behavior. Bad connections in the powersupply, system controller, or tuner, may result in this sort of behavior.See the section: "TV and monitor manufacturing quality and cold solderjoints". See the sections and separate documents on problems withRCA/GE/Proscan and Sony TVs if yours is made by one of these companies. A microcontroller or other electronic problem is also possible. If thesymptoms only develop after the set warms up, it may be heat related (thoughsimple bad connections are more likely). Use 'circuit chiller' or a heat gunto identify the bad part. Wiring transmitted interference:------------------------------- The power that comes from the wall outlet is supposed to be a nice sinusoidat 60 Hz (in the U.S.) and it probably is coming out of the power plant.However, equipment using electric motors (e.g., vacuum cleaners), fluorescentlamps, lamp dimmers or motor speed controls (shop tools), and other high powerdevices, may result in a variety of effects. While TVs normally include some line filtering, the noise immunity varies.Therefore, if the waveform is distorted enough, some effects may show up evenon a high quality TV. Symptoms will usually be one or two areas of noise moving slowly up the screen. The source is probably local - in your house and probably on the same branchcircuit - but could also be several miles away. * The rate will be the difference between the power line frequency (60 Hz in the U.S.) and the scan rate (59.94 Hz for NTSC). This results in a drift of about 16 seconds for a complete cycle (8 seconds if the inteference is at 120 Hz). - A single bar would indicate interference at the power line frequency. - A pair of bars would indicate interference at twice the power line frequency. Either of these are possible. * Try to locate the problem device by turning off all suspect equipment to see if the problem disappears. * The best solution is to replace or repair the offending device. In the case of a light dimmer, for example, models are available that do a better job of suppressing interference than the typical $3 home center special. Appliances are supposed to include adequate noise suppression but this is not always the case. If the source is in the next county, this option presents some significant difficulties :-). * Plugging the TV into another outlet may isolate it from the offending device enough to eliminate or greatly reduce the interference. * The use of a line filter may help. A surge suppressor is NOT a line filter. * Similar symptoms could also be produced by a defective power supply in the TV or other fault. The surest way of eliminating this possibility is to try the TV at another location. Jittering or flickering due to problems with AC power:----------------------------------------------------- If you have eliminated other possibilities such as electromagneticinterference from nearby equipment or a faulty video cable or problemswith the video input (e.g., cable or VCR) - then noisy or fluctuating ACpower may be a possibility. However, most modern TVs usually have wellregulated power supplies so this is less common than it used to be. Thenagain, your TV may just be overly sensitive. It is also possible thatsome fault in its power supply regulator has resulted in it becoming moresensitive to small power fluctuations that are unavoidable. One way to determine if the problem is likely to be related to AC poweris to run the TV on clean power in the same location connected to thesame video input. For example, running it on an Uninterruptible Power Source(UPS) with the line cord pulled from the wall socket would be an excellenttest. The output of the UPS's inverter should be free of any power linenoise. If the TV's image has now settled down: 1. Large appliances like air conditioners, refrigerator, or washing machines on the same circuit might cause significant power dips and spikes as they cycle. Plugging a table lamp into the same outlet may permit you to see any obvious fluctuations in power. What else is on the same circuit? Depending on how your house or apartment is wired, the same feed from the service panel may be supplying power to widely separated areas. 2. For some unfathomable reason, your TV may just be more sensitive to something about the power from the circuit in that room. There may be nothing actually wrong, just different. While unlikely, a light dimmer on the same circuit could be producing line-conducted interference. If you have a multimeter, you could at least compare the voltages between the location where it has problems and the one where it is happy. Perhaps, the TV is sensitive to being on a slightly different voltage. This might only be a problem if some circuitry in the the TV is marginal in some respect to begin with, however. 3. There could be a bad connection somewhere on the circuit. If your house has aluminum wiring, this is a definite possibility. Try a table lamp since its brightness should fluctuate as well. This should be checked out by a competent electrician as it represents a real fire hazard. An electrician may be able to pinpoint the cause but many do not havethe training or experience to deal with problems of this sort. Certainly,if you find any power line fluctuations not accounted for by majorappliances, on the same circuit this should be checked by an electrician. TV blows fuses or trips breakers or worse when A/V connections are made:----------------------------------------------------------------------- You have sent the TV for repair and now three times, it blows somethingthe instant anything is connected to it in your house. Other A/V equipmentoperates fine. Assuming all the other stuff is plugged into the same outlet asn is 115 VACequipment and that thsi happens instantly when the TV is connected: Next time they bring it back, measure the voltage between the A/V connectorshields and the shields on your cables - I wouldn't be surprised to find somesubstantial fraction of 115 VAC between them. This would mean that there isan internal short in the TV (their problem - any competent service center willroutinely check for signal-AC ground shorts) resulting in a connection betweenthe non-isolated AC ground and the signal ground. When you connect yourequipment, you complete a path which results in a short circuit. Dependingon the design of the TV and where the fault lies, much more than a simplefuse may be destroyed. This is similar to connecting a scope probe groundto a live chassis TV - see the section: "Safety guidelines". My TV has the shakes:-------------------- You turn on your TV and 5-10 seconds later, the display is shaking orvibrating for a second or so. It used to only occur when first turned on,but now, the problem occurs 3 times in 30 seconds. Of course, manyvariations on this general theme are possible. Some possibilities: 1. External interference - did you change anything or move your A/V setup recently? Do you have a computer monitor nearby? 2. Defective circuitry in TV - power supply regulation, deflection, or bad internal connections are possible. 3. Defective video cable (unlikely) - wiggle the cables to be see if you can induce the problem. 4. Loose trim magnets of other magnetic components on or near deflection yoke. This is somewhat rare but if the adhesive comes apart, the magnetic fields from the deflection current can cause the parts to vibrate which will result in a jitter or movement of the picture. There may even be audible crackling or snapping sounds associated with this vibration. Note that many of the sources of electromagnetic interference that areproblems with computer monitors like transformers and power lines willnot cause noticeable shaking, wiggling, or jiggling on a TV because thepower line and vertical scan are at almost exactly the same frequencyand any such movement would be very slow. TV displays black box with normal picture border:------------------------------------------------ When the set is first turned on, it works fine for about 20-30 seconds, thenthe picture goes away - all but about 1 inch of picture all around the outeredge of the screen. The square ring of picture that is left, is dim butotherwise normal. (The following from: (jack haney) jhaney@pacifier.com)) If this is a newer set, this sounds very much like a "closed caption" box for a captioning system not being used in your area.Newer Mitsubishis do much the same thing. If the wrong caption typeis selected inadvertantly, all you'll see is a large black boxon screen taking up about all but an inch each way.Try turning offall closed caption. The first time I saw this I looked like a damnfool in front of a customer, took me 30 minutes to figure it out. Advertising overload:-------------------- "I noted the advertsing programs put in bright several frames of overshooting white signals in purpose of attracting attention which I do not want also it gets on my nerves sometimes. *flash* *flash* Ughhh! Is there a way to cutoff the "overload" or tone down that?" (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). Technically, the TV takes care of its own overload protection. Or at least it*should*, on some TV's you will certainly observe the line transformer goinginto saturation for a while. Other than that there is not much you can do,each TV should represent its input signals with as much fidelity as possible.Change channels? (I already suggested not watching :-). --- sam). Strange codes appearing on TV screen:------------------------------------ "I've seen this sort of thing on a TV I bought a couple of years ago. I only see it when Proctor & Gamble ads are on. The newer TVs are required to have Closed Caption decoding (CCD). My TV has an OFF-ON button for CCD. It also has a button labeled CH1-CH2. When pushed in I get the verbal text on the screen like I should. When the button is out, I get the funny codes from Proctor & Gamble." (From: Tim (jollyrgr@mc.net)). The code you are seeing is Closed Caption 2. My Zenith has CC 1, 2, 3, 4,as well as Text 1, 2, 3, and 4. I have seen CC 1 which is the normal closedcaptions. CC 2 is used for commercial logging/identification. There shouldbe a way to completely turn off the captions. The TV, as you state, has aswitch for turning off the captions and should solve your problem. Releasing 'demo' mode:--------------------- You really want to watch CNN but the TV insists on promoting itself: * For Fisher TVs: (From: Alan (algba@ix.netcom.com)). Hold down the menu key on the remote for 8 seconds to switch it out of that mode or back in again. * For Magnavox TVs: (From: L. Tankersley (boat39@mail.idt.net)). Try pressing both volume control buttons on the TV at the same time and releasing. The demo mode should go off and the set turn off by itself. Turn the set back on and it should be back to normal. * For Sanyo TVs: (From: Bill A. (Lucy27@ix.netcom.com)). Try pressing the "menu" button on the unit and keep it depressed for about 15 to 20 seconds. This should release the demo mode. TV was rained on:---------------- Was the set plugged in when the leak started? Any piece of equipment withremote power-on capability has some portions live at all times when pluggedin and so there may have been damage due to short circuits etc. Substantialdamage could be done due to short circuits. Otherwise, you may just need to give it more time to dry out. I havehad devices with keypads getting wet that required more than a week butthen were fine. There are all kinds of places for water to be trapped andtake a long time to evaporate. If the set got wet while unplugged (in a leaky attic or wet basement), forexample, or it has a pull or click knob on/off switch, then give it timeto dry out - completely. Assuming all visible water is drained, a weekrepresents a minimum safe time to wait. Don't rush it. Generally, some moisture will not do any permanent damage unless theset was on in which case you will simply have to troubleshoot it theold-fashioned way - one problem at a time. TV was dropped:-------------- You have probably seen the TV advertisements - I don't recall what theywere for - where a late model TV is dropped out a many story windowon a bunjie cord to rebound once undamaged and without hitting a baby ina stroller but then smash to smithereens on the sidewalk once the strollerhad moved. Needless to say, this is generally not a recommended way totreat a TV set! However, mishaps do happen. Assuming it survived mostly intact - the CRT didn't implode, you could stillhave a variety of problems. Immediately unplug the set! If you take it in for service, the estimate you get may make the national debtlook like pocket change in comparison. Attempting to repair anything that hasbeen dropped is a very uncertain challenge - and since time is money for aprofessional, spending an unknown amount of time on a single repair is veryrisky. There is no harm is getting an estimate (though many shops charge forjust agreeing that what you are holding was once - say - a TV, or was it afishtank?) This doesn't mean you should not tackle it yourself. There may benothing wrong or very minor problems that can easily be remedied. Thefollowing are likely possibilities: 1. Cracked circuit boards. These can be repaired since TVs usually have fairly wide open single or two sided boards. 2. Broken circuit components. These will need to be replaced. 3. Broken solder connections particularly to large heavy components on single sided boards. Reflow the solder. If the trace is cracked or lifted, repair as in (1). 4. Broken mounting brackets. These are usually made of cheap plastic and often don't survive very well. Be creative. Obtaining an exact replacement is probably not worth the trouble and expense. 5. Components knocked out of line on the CRT envelope or neck - deflection yoke, purity magnets, convergence magnets and coils, geometry correction magnets. These will need to be reattached and/or realigned. Some CRTs use little magnets glued to the funnel portion of the CRT envelope. If any of these have come loose, it could be quite a treat to figure out where they went and in what orientation. 6. Internal damage to the CRT - popped or distorted shadow mask, misaligned electron guns. Unfortunately, you will probably have no way of identifying these since you cannot see inside the CRT. They will not be apparent until all other faults have been remedied and the TV set is completely realigned. At that point, extremely severe purity or convergence problems that do not respond to the normal adjustment procedure would be one indication of internal damage. Give the TV a nice funeral. To test to see if it is a chroma problem - disconnect (or disable) twoof the 3 primary colors with a B/W picture or solid raster displayed. Ifthe raster is not now a pure color, you have a CRT or CRT purity adjustmentproblem. If you still want to tackle a restoration: As noted, unplug the TV even if it looks fine. Until you do a thoroughinternal inspection, there is no telling what may have been knockedout of whack or broken. Electrical parts may be shorting due to a brokencircuit board or one that has just popped free. Don't be temptedto apply power even if there are no obvious signs of damage - turningit on may blow something due to a shorting circuit board. If it is aportable, remove the batteries. Then, inspect the exterior for cracking, chipping, or dents. In additionto identifying cosmetic problems, this will help to locate possible areas tocheck for internal damage once the covers are removed. Next, remove the cover. Confirm that the main filter capacitors arefully discharged before touching anything. Check for mechanical problemslike a bent or deformed brackets, cracked plastic parts, and anything thatmay have shifted position or jumped from its mountings. Inspect for looseparts or pieces of parts - save them all as some critical magnets, forexample, are just glued to the CRT and may have popped off. Carefully straighten any bent metal parts. Replace parts that wereknocked loose, glue and possibly reinforce cracked or broken plastic.Plastics, in particular, are troublesome because most glues - even plasticcement - do not work very well. Using a splint (medical term) or sistering(construction term) to reinforce a broken plastic part is often a goodidea. Use multiple layers of Duco Cement or clear windshield sealerand screws (sheetmetal or machine screws may be best depending on thethickness and type of plastic). Wood glue and Epoxy do not work wellon plastic. Some brands of superglue, PVC pipe cement, or plastic hobbycement may work depending on the type of plastic. Inspect for any broken electronic components - these will need to be replaced.Check for blown fuses - the initial impact may have shorted somethingmomentarily which then blew a fuse. There is always a risk that the initial impact has already fried electronicparts as a result of a momentary short or from broken circuit traces andthere will still be problems even after repairing the visible damage and/orreplacing the broken components. This is most likely if the set was actuallyon but most modern TVs have some circuitry energized at all times. Examine the circuit boards for any visible breaks or cracks. These willbe especially likely at the corners where the stress may have been greatest.If you find **any** cracks, no matter how small in the circuit board, youwill need to carefully inspect to determine if any circuit traces runacross these cracks. If they do, then there are certainly breaks inthe circuitry which will need to be repaired. Circuit boards in consumerequipment are almost never more than two layers so repair is possible butif any substantial number of traces are broken, it will take time and patience.Do not just run over them with solder as this will not last. Use a finetipped low wattage soldering iron and run #22-26 gauge insulated wiresbetween convenient endpoints - these don't need to be directly on eitherside of the break. Double check each connection after soldering for correctwiring and that there are no shorts before proceeding to the next. If the circuit board is beyond hope or you do not feel you would be ableto repair it in finite time, replacements may be available but their costis likely to be more than the equipment is worth. Locating a junk unit of thesame model to cannibalize for parts may be a more realistic option. Degauss the set as any impact may magnetize the CRT. Power cycling maywork but a manual degaussing is best. Once all visible damage has been repaired and broken parts have been replaced,power it up and see what happens. Be prepared to pull the plug if thereare serious problems (billowing smoke or fireworks would qualify). Perform any purity, convergence, or other realignment as needed. Then proceed to address any remaining problems one at a time. Really cleaning a TV inside and out:----------------------------------- (This was written for computer monitors but applies equally well to modernTV sets.) (From: Dr. Ludwig Steininger (drsteininger@t-online.de)). Often I get defective monitors, which are more than 5 years old, and have been run in offices for 8 to 10 hours/day. So, their case and pcbs usually are verydirty and dusty. What do I do (it's no joke!): After removing the case I carefully put them ina bath (on a flexible layer) and let them have a intensive shower of pure coldwater (for 1 to 2 minutes). Additionally, the case is cleaned with soap or adetergent containing liquid (being careful, not to spill to much of it ontothe PCBs). After rinsing with fresh clear water, dust and other kinds of dirtare removed and the monitors look new again. Then I allow all drops of waterto run off. This can effectively be supported by turning the monitor onanother side from time to time (duration: approximately 1 hour). Beforeturning on AC again, I let the wet monitor dry in ambient air for about 2 days(in the sunshine this can be finished in 1 day only). This procedure has been applied for many monitors. I've never had any bad experiences (it's very important to wait, until the pcbs are really dry!). Considering this experience, I just can't imagine, that it might not be possible, to "save" a TV set or computer monitor, which has been drowned or some liquid has been spilled, and AC has been plugged off ASAP (although I've never had such a case). I think, that in such a case, it's important to have arapid shower in order to prevent corrosion and deposits. By the way: I know a German company, which uses water from cleaning PCBs of computer hardware for cleaning them after being contaminated by smoke from a fire. So, in case of spillage, one has nothing to loose. Just try to shower your monitor or TV set! Setup menus will not go away or hieroglyphics on screen:------------------------------------------------------- Both these problems could be caused by a faulty microcontroller orits associated circuitry. However, bad connections in the vicinityof the controller logic could also be at fault. Unless you see something obvious, you will need schematics. Setup adjustments lost - TV service codes:----------------------------------------- Many modern TVs have RAM, somewhat like the CMOS SETUP memory in your PC,that store all factory adjustments. When power is lost, there is powersurge, lightning strike nearby, nuclear detonation or EMP, it mayhave put bad information into the ram and thrown it out of adjustment. Thereis a way to get into the service mode (depress and hold a secret buttondown and turn set on, special combination of buttons on the remote, etc.)and then use the remote to reinitialize and adjust the problems out. HOWEVER, IF YOU DON'T KNOW WHAT YOU DOING YOU COULD GIVE YOURSELF WORSEPROBLEMS. YOU COULD EVEN BLOW VERY EXPENSIVE PARTS WITH SOME SETS! Try not to make any unnecessary changes and document every change you make!!!That way you can go back if you do anything wrong (hopefully). However, somechanges - even if nothing fails - will result in an unviewable picture thusmaking it extremely difficult to see what you are doing. The Sams' Photofact manual for your set should describe this process - you maybe able to get Photofacts from a local library, or you can buy them from RadioShack or a place like MCM Electronics or an electronics distributor. TheJune, 1998, issue of "Electronic Servicing and Technology" (ES&T) had anarticle on service mode if you have access to this publication (it won't bein your public library). Some examples follow. You would need to check the service information foryour specific model to be sure. However, trying the procedures describedbelow probably will not hurt. The TV will just ignore you if it doesn'tlike your codes! However, if you do get in, make sure you know what you aredoing or your original problem may be inconsequential compared to your newones! * Ferguson/Thomson Technology T49F television (TX91 chassis and probably others as well). (From: Peter Radlberger (peter.radlberger@blackbox.at)). - Unplug SCART cable. - Switch to Standby, then switch mains off. - Hold blue button on remote, power up. - Repress blue button, service screen appears. - Select function with blue, adjust with Vol+/-, store new value with highlighted Memo and Vol+. Restore jumps to original value, ROM are production defaults. - Leave with Standby. * Some JVC models (JA chassis): (From: Roger Dowling (rogerd@globalnet.co.uk)). Press the DISPLAY key and the CINEMA/GAME key of the remote control simultaneously. * Some JVC models: (From: Andy Cuffe (baltimora@psu.edu)). I have used this on JVCs from 1995: - Set the clock to 3:21 AM. - Start the clock as you normally would but press MUTE while "Thank you" is flashing. - Press menu up or down just after MUTE. - Use up/down to select options and left/right to adjust. The settings are automatically saved when you exit. (From: P. White (pwhite4@aol.com)). On the new line of JVC sets, hold the "Display" and "Video Status" buttons on the remote simultaneously. The set will bring up a service menu. Good luck trying to navigate the service menus with out a manual. * Some Magnavox models: Enter 062596 then MENU. The channels will change but when MENU is pressed, the TV will enter the service menu. (From: Gscivi (gscivi@aol.com)). Hit MENU on the remote, while the menu is still up press the numbers 061596 or 061597. One of these will bring up the service menu. Now, your right/left arrows on remote will switch between the numbers across the bottom of the screen, highlight the number set right after the 'setup or service' option. The arrow up/down will change to the next service position. * Some Mitsubishi models: Use your remote and press MENU then 2357 use VIDEO to select service menu and ADJUST to set values. * Some Nokia (ITT) models: (From: Stefan Huebner (Stefan.Huebner@rookie.antar.com)). Press mono/stereo - Channel C - Hypersonic within 1 second, The display now shows SE. Leave the service mode with the standby button. * Nokia model 6363: (From: Ian Abel G3ZHI (bert@skypilot.demon.co.uk)). Nokia model 6363 (and probably other late model TVs) - On the remote press -/-- then menu then TV all within 1 second. When in setup mode you use channel up or down buttons on the TV set to change to whatever you need to set up. Adjustments are made with volume + and - buttons on the remote control. My advice is to make a note of all the settings before making changes then you can always go back to them. * Some Panasonic models: A very detailed document on Panasonic Service(man) mode for some models in the GL10C family (may apply to others as well) is provided at: - http://www.colpetzer.com/calanan/Panasonic/ Includes entering/saving/leaving, register contents and range, etc. * Panasonic TX-W28R3 (and similar models): (From: Arpad Kothai (arpadk@EUnet.yu)). The remote control is used for entering and storing adjustments, with the exception of cut-off adjustments which must always be done prior to service adjustment. Perform adjustments in accordance with screen display. The display on the screen also specifies the CCU variants as well as the approximate setting values. The adjustment sequence for the service mode is indicated below. 1. Set the Bass to maximum position, set the Treble to minimum position, press the Reveal on the remote control and at the same time press the Volume on the customer controls at the front of the TV, this will place the TV into the Service mode. 2. Press the RED/GREEN buttons to step down / up through the functions. 3. Press the YELLOW/BLUE buttons to alter the function values. 4. Press the STORE button on the preset panel after each adjustment has been made to store the required values. 5. To exit the Service Mode press the Normalization button. * Philips 29PT8303 and other similar models: Using the remote control, press 062596, then the MENU key. * Some RCA models: The codes can be found pasted to the inside of the back cover. To get into the SETUP MENU, "Press and hold MENU, hit POWER and then VOL+. DO NOT set H Freq too low or you will wipe the EEPROM. Bummer. For more information, see the document: "RCA/GE TV (CTC175/176/177) Solder Connection and EEPROM Problems" * Some Samsung models: (From: Livio Belac (lbelac@efpu.hr)). - CHASSIS: SCT51A: PICTURE OFF (ST. BY) -> SLEEP -> P.STD -> MUTE -> PICTURE ON (PWR ON). - CHASSIS: SCT11A, SCT11B, SCV11A, SCV11B ST. BY -> P.STD -> MENU -> SLEEP -> POWER ON. Perform adjustments with VOL +/- Select between adjustments with CH +/- * Some Sharp models (including 19J-M100 and 20J-M100): Press the 'vol up' and 'channel up' at the same time and then plug in the set to AC line. Use the 'channel up/down' buttons to select the register; use the 'vol up/down' buttons to select the values. To exit this mode, depress the 'power' button. * Various Sony models: Service mode adjustments can be found at: - http://www.repairfaq.org/REPAIR/F_Sony_setup.html. * Another Sony: (From: Trygve Pedersen (trygve-p@netpower.no)). To enter service mode turn off power push both + and - buttons on front of TV while you powers up you get TT on screen, and then you enter 34 (TT34 on screen), press the left arrow twice on remote, and you are in service mode. * Some Sony UK models: Fast text buttons operate service mode. * Sony KV-X2571 and similar models: (From: Peter & Jolanda Faber (pfaber@worldonline.nl)). Switch TV off. Press and hold two switches (center & right) under front panel. Switch set on with main switch. Wait a few seconds. Release two switches again. * Some Toshibas: (From: Bill A. (Lucy27@ix.netcom.com)).: 1. Press the mute button on your remote and release (put unit in mute). 2. Press and hold mute button on remote. 3. At the same time while holding mute button on remote, press the menu button on the TV itself. If done correctly an "s" should show up on the screen to determine that you have successfully entered the service mode. 5. Now, I believe if you press the menu button again on the unit some microprocessor data should be showing up on screen i.e. current micro part# etc. 6. Press #9 on remote to enter various modes of operation. Here is where you really need the service manual, too much info to show here. Once in Service mode be very careful!!! * Zenith System 3: (From: Raymond Carlsen (rrcc@u.washington.edu) and jollyrgr@mc.net). Hold the MENU button down for about 5 seconds... until the currently displayed menu disappears. Then press 9 8 7 6, then ENTER. There are two menus in the service mode. Use the MENU to toggle between them. Press SELect until the item you want is highlighted, then the ADJ button (left or right) for the submenu or the adjustment. Press SELect for the next item and MENU for the alternate menu. Press ENTer to exit the service mode. Service menu caution:-------------------- Even changing a parameter which results in the loss of the picture couldrequire replacing the EEPROM if you cannot get the set to come on and viewthe service menu to reset! However, it may be possible to drive the HOT with an external sourceso you can see the menus for setup. CAUTION: there is some risk. Should drive the HOT with too low a frequency,it may blow due to flyback core saturation. Use a series light bulb tominimize this possibility. Strange number in upper left corner in Magnavox service mode:------------------------------------------------------------ "When I put my Magnavox in service mode a number comes up on the top left of the screen. I see no description of it in the service manual. Is this an hours used timer? Is it actually in hours?" (From: Mister M. (mister-m@ix.netcom.com) and zapper (zap@mhv.net)). This is actually a usege timer in hexidecimal. Hey, at least it is not binary --- sam :-). TV doesn't work after being in storage:-------------------------------------- So the TV you carefully stuffed in a corner of the garages is now totallydead. You swear it was working perfectly a year ago. Assuming there was absolutely no action when you turned it on, this hasall the classic symptoms of a bad connection. These could be cold/crackedsolder joints at large components like transformers, power resistors, orconnectors and connectors that need to be cleaned or reseated. By 'no action'I mean not even a tweet, bleep, or crackle from anything. To narrow it down further, if careful prodding with a well insulated stickdoes not induce the set to come on, check the following: 1. Locate the horizontal output transistor. It will be in a TO3 metal (most likely on an older set) or TOP3 plastic package on a heat sink. With power off, measure collector to emitter with an ohmmeter - in at least one direction it should be fairly high - 1K or more. Then clip a voltmeter on the 250 V DC or higher scale across C-E and plug in and turn on the set. Make sure it is well insulated. * If the problem is in the low voltage (line) power supply, there will be no substantial voltage across C-E. You should be able to trace from the power line forward to find the bad part though a schematic will help greatly. * If the problem is in the startup circuit or horizontal oscillator/driver, then there will be something on the order of 100-160 V across C-E. In this case, a schematic may be essential. Note: don't assume that the metal parts of the chassis are ground - theymay be floating at some line potential. There is also a slight chance that there is a low voltage regulatorin addition to the horizontal output, so don't get them confused. Thehorizontal output transistor will be near the flyback transformer andyoke connector. Older TVs with multiple intermittent problems:--------------------------------------------- If the set is say, a GE, with a manufacturing date around 1980, it is possibleyou have one of those circuit boards best described as bad solder jointsheld together with a little copper. In this case, prodding may get the set started. The circuit boards in these sets were double sided using whatwere called 'rivlets' for vias. The rivlets were relatively massive -literally little copper rivets - and they were not adequatelyheated during assembly so there were bucketloads of cold solder jointsthat showed up during middle age. I repaired one of these by literallyresoldering top and bottom of every one of the darn things with a highwattage iron. TV has burning smell:-------------------- Assuming there are no other symptoms: If this appears after extended operation - an hour or more - it mayjust be a build up of dust, dirt, and grime over the years. Afterunderstanding the safety info, some careful vacuuming inside may help.Just don't be tempted to turn any screws or adjustments! Dust is attracted to the high voltage section in particular - even thefront faceplate of the CRT collects a lot and should be wiped with a dampcloth from time to time. If the symptoms develop quickly - in a few minutes or less, then therecould still be a dust problem - a power resistor may be heating a wad ofit but other possibilities need to be considered. If not dust, then probably in the power supply but realize that TVs don'thave a nice metal case labeled 'power supply'. It is just a bunch of stuffscattered around the main board. Without identifying the part that isheating, a diagnosis is tough especially if the set really doeswork fine otherwise. However, if a series regulator were faulty and puttingout too much voltage, the set could appear to work properly but in facthave excessive power dissipation in certain components. If cleaning the dustdoes not solve the problem, you will probably need a schematic to identifythe correct voltages. Static discharge noise and picture tube quality:----------------------------------------------- "I bought a 29" TV a couple of weeks ago and I have noticed that after being switched on for > about 15/20 minutes, whenever the picture changes from a "light" scene to a darker scene, the set makes a crackling noise. It sounds as though there has been a build-up of static and it is being discharged. I have never noticed this in a TV before and I was wondering if this is normal and acceptable behaviour for a large-screen TV?" (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). It probably is normal. Whether it is acceptable is a personal matter. Insome geographic areas no countermeasures are taken at all... When the scene changes from bright to dark, the beam current is reduced topractically zero. As a result, the high voltage rises. (The high voltagesupply has a relatively high internal impedance.) The high voltage isconnected to the inside layer of the picture tube. A voltage change on theinside will also cause a voltage change on uncovered parts of the outside,especially on the part of the picture tube that is hidden under the deflectioncoils. This causes little sparks between the picture tube surface and theinside of the deflection coils and this is accompanied by a crackling sound. On the better picture tubes, a dark "anti-crackle coating" is painted on thepicture tube near the deflection coil. This is a very high impedance coating,dark black, much darker than the usual aquadag coating over the rest of thepicture tube. You should be able to see the difference. If, on the other hand, the outside of the picture tube near the deflectioncoil is not coated then you have a problem. Then you will hear strongcrackling also at switch-on and switch-off. Normally you shouldn't see such a'cheap' picture tube on the European market... The area of the picture tube around the anode connector is also not coated,for obvious reasons. Normally that should not cause any significantsound. Same goes for the front of the screen and neither should the anodecable crackle. In a dark room you should be able to see from the tiny blue flashes where thesound comes from. This is perhaps best observed at switch-on and switch-off(with a black picture on the screen). Try and keep the back cover mounted ! Revival of dead or tired remote control units:--------------------------------------------- There are two types of problems with hand held remote controls: theyhave legs of their own and they get abused or forgotten. I cannothelp you with walking remotes. Where response is intermittent or the reliable operating distance isreduced, first check the batteries and battery contacts. If some buttonsare intermittent or dead, than the most likely cause is dirty or worncontacts under the rubber buttons or on the circuit board. If there is no response to any functions by the TV or VCR, verify that anymode switches are set correctly (on both the remote and the TV or VCR).Unplug the TV or VCR for 30 seconds (not just power off, unplug). Thissometimes resets a microcontroller that may have been confused by apower surge. Confirm that the remote has not accidentally been set toan incorrect mode (VCR instead of TV, for example). If it a universaltype, it may have lost its programming - reset it. Make sure you areusing the proper remote if have multiple similar models. Test the remote with an IR detector. An IR detector card can be purchasedfor about $6. Alternatively, build the circuit at the end of this document.If the remote is putting out an IR signal, then the remote or the TV or VCR mayhave forgotten its settings or the problem may be in the TV or VCR and notthe hand unit. The following is just a summary - more detailed informationis available in the companion document: "Notes on the Diagnosis and Repair ofHand Held Remote Controls". Problems with remote hand units: All except (1) and (2) require disassembly - there may be a screw or two andthen the case will simply 'crack' in half by gently prying with a knife orscrewdriver. Look for hidden snap interlocks. 1. Dead batteries - solution obvious. 2. Corroded battery contacts, Thoroughly remove chemical deposits. Clean contacts with pencil eraser and/or sandpaper or nailfile. 3. Broken connections often between battery contacts and circuit board, possibly on the circuit board - resolder. 4. Bad resonator or crystal - replace, but diagnosing this without an oscilloscope may be tough. Broken connections on resonator legs are common. 5. Dirt/spills/gunk preventing keys from operating reliably. Disassemble and wash rubber membrane and circuit board with water and mild detergent and/or then alcohol - dry completely. 6. Worn or corroded contact pads on circuit board. Clean and then use conductive Epoxy or paint or metal foil to restore. 7. Worn or dirty pads on rubber keypad. Clean. If worn, use conductive paint or metal foil to restore. 8. Cracked circuit board - can usually be repaired as these are usually single sided with big traces. Scrape off insulating coating and jumper breaks with fine wire and solder. 9. Bad LED. If IR tester shows no output, remove LED and power it from a 9V battery in series with a 500 ohm resistor. If still no output, replace with readily available high power IR LED. Otherwise, check driver circuits. 10. Bad IC - if it is a custom chip, forget it! Failure of the IC is usually quite unlikely. (The following is from Duane P Mantick:) An awful lot of IR remotes use IC's from the same or similar series. A common series comes from NEC and is the uPD1986C which, incidentally is called out in the NTE replacements book as an NTE1758. A lot of these chips are cheap and not too difficult to find, and are made in easy-to-work-with 14 or 16 pin DIP packages. Unless you have no soldering or desoldering skills, replacement isn't difficult. There are a large variety of universal remotes available from $10-$100. Forgeneral TV/VCR/cable use, the $10 variety are fine. However, the preprogrammedvariety will not provide special functions like programming of a TV or VCR.Don't even think about going to the original manufacturer - they will chargean arm and a leg (or more). However, places like MCM Electronics do stock avariety of original remotes - prices range from $9 - $143 (Wow $143, for justa stupid remote! It doesn't even have high definition sound or anythingexotic). The average price is around $40. Problems with the IR remote receiver:------------------------------------ Although the hand unit is most likely to be the cause of any problemswith the remote control, it is also possible for the IR receive moduleto fail or for power to it to be missing. Microcontroller problems aswell can result in similar symptoms. First confirm that the hand unit is putting out the correct code. If itis a programmable type, try re-entering the settings for your TV. Installa set of fresh batteries. Try a different remote if possible. Use an IRdetector to verify IR emissions (see the section: "Revival of dead or tiredremote control units"). The IR receiver is often a self contained module connected to the rest ofthe TV's circuitry by 3 wires: Power (+12 V typical), Ground, and Signal Out. The IR receiver module will be located directly behind the IR window. Testby confirming that DC power is present. A schematic will tell you exactlywhat it should be but figure on 6 to 12 V if you do not have one. If thisis present and you have an oscilloscope, put is on the Signal Out. You shouldsee the demodulated data stream corresponding to whatever key is pressed onthe hand unit. It should be a logic level signal swinging between 0 andthe supply or +5 volts. If there is no power, then a bad cable connection or blown fusable resistormay be the cause. If there is correct power but no signal, a fault internalto the IR module is likely. The internal circuitry may be a combinationof special ICs and discrete components. The Sams'' or service manual may ormay not provide the details. There may be an adjustment for the carrierfrequency but don't be tempted to touch this unless you have exhasutedother possibilities - and them mark it first! If the signal is present, then there may be a problem in the microcontrolleror other logic on the mainboard. This will require a schematic to proceedfurther. So you lost your original remote (or it fell in the toilet):----------------------------------------------------------- An exact replacement remote will be easiest to use but may do significantharm to your bank account. For example, you cannot add or remove channels from a typical Sony TV usingthe common universal remotes. (From: Ed Ellers (edellers@delphi.com)). Universal Electronics' "One For All" remote controls can reproduce thesecodes, and any others on any Sony TV (among others). Typically you'd press[MAGIC] and then 1-9-4 to add a channel or 1-9-0 to erase one; to start theauto program mode you'd press [MAGIC] and then 1-2-4. Loudspeakers and TVs:-------------------- Loudspeakers incorporate powerful magnets - the larger the speaker, thelarger the magnet. However, anyone who goes ballistic when the mentionis made of a loudspeaker near a TV or monitor, should take their Vallium. The fringe fields outside the speaker box will not be that great. Theymay affect the picture perhaps to the point of requiring degauss. Thenormal degauss activated at power-on will usually clear up any color purityproblems (assuming the loudspeakers have been moved away). At worst, manualdegauss will be needed. The CRT will not be damaged. The maximumfield - inaccessible at the voice coil - is quite strong. However, evenfor non-shielded loudspeakers, the magnetic field decays rapidly withdistance especially since the core structure is designed to concentrateas much of the field as possible in the gap where the voice coil travels. However, keeping speakers away from CRTs is a good idea. Now, you really should keep your superconducting magnetic resonance imagermagnet at least in the next room..... Should I replace all the electrolytic capacitors if I find a bad one?:--------------------------------------------------------------------- When a bad capacitor is found in a TV, the question of course arisesas to the likelihood of other capacitors going bad in short order.It might be worth checking (other) caps in the power supply or hot(temperature) areas but you could spend you whole life replacing **all**the electrolytics in your older equipment! Sweet little old ladies and TVs from attic:------------------------------------------ Always confirm the customer's complaints first!! Then verify thateverything else works or you will never know if your efforts haveaffected something unrelated. (Original request from rogerj@apex.com): >A sweet little old lady has duped me into repairing her old G.E. 13" color>TV. Wanted me fix bad volume pot..... "oh it has such a good picture"...>she says. >Stupidly w/o even turning it on, (big mistake) I begin to open the set.>After 15-20 min. of travail, I discover that a previous "repairman" has glued>the case shut! >Now w/ set open, I turn it on and this picture is LOUSY. Bad color, and very>poor convergence. But I don't know if I'm to blame for banging it around >trying to open it up. Also, no horizontal or vertical hold. (fixed that>wiht a few caps). This thing has probably been sitting around for a few>years. Well, you certainly did not kill the caps. Anything that sits for a fewyears - probably in a damp unheated attic - is suspect. Did you find the adjustments on the yoke assembly tight? If so, you probablydid not move anything very much either. She may remember the good pictureit produced before being stuffed away in the attic. > Anyway after going through all the adjustments, the convergence at the sides> is still bad and the horizontal size is a tad insufficient (w/no adjustment> available) Could be that the convergence (including pincushion) circuits are stillfaulty - not just misadjusted. Other things that can effect horizontal size while still giving you a completepicture: 1. Voltage to horizontal output transistor low. Is there a voltage regulator in your set? The one I have has none. I assume your line voltage is ok. 2. Increased resistance or inductance of the yoke windings. For all you know, the yoke may have been replaced with the wrong part. 3. Yoke improperly positioned on tube neck. 4. Excessive high Voltage. This is usually not adjustable. I bet the thing hasn't worked properly in 10 years. Phantom spot or blob on CRT after set is shut off:------------------------------------------------- (Portions of the following from a video engineer at Philips.) Why is there a splotch of colored light at the center of the CRT afterI kill power to my TV? Why does this not happen if the plug is pulledinstead? It seems to last for hours (well maybe minutes at least). A broad diffused glow (not a distinct spot in the middle of the screen)that lasts for a few seconds to minutes is called 'afterglow' and may beconsidered 'normal' for your model. The warm CRT cathodes continue toemit electrons due to the high voltage that is still present even thoughthe signal circuits may have ceased to operate. For more sharply defined spots there are two phenomena: 1. Thermal emission from a cathode that has not yet cooled off (and this could take several minutes) gives a more or less circular spot near the centre. It is actually 3 spots from the 3 cathodes, we at Philips call them 'Christmas balls'. 2. Field emission from sharp whiskers on any electron gun part gives a much sharper spot, sometimes with a moon-shaped halo around it. Even with the filament off, there may be some electron emission from these sharp points on the cold cathode(s) due to the strong high voltage (HV) electric fields in the electron gun. I do not know how likely this is or why this is so. The shape of the spot is an inverted image of the shape of the emittingarea(s) on the electron guns cathodes. The visibility of both effects depends in the same way on the decay time ofthe high voltage (HV/EHT) on the anode. When turned off with the remote or front panel button, you are not actuallykilling AC power but are probably switching off the deflection and signalcircuits. This leaves the HV to decay over a few minutes or longer as itis drained by the current needed to feed the phantom spot or blob. When you pull the plug, however, you are killing AC input and all the voltages decay together and in particular, the video signal may be presentfor long enough to keep the brightness (and beam current) up and drain theHV quickly. Whether this actually happens depends on many factors - oftennot dealt with by the designers of the set. A proper design (who knows, yours may simply have been broken from day 1 orsimply be typical of your model) would ensure that the HV is drained quicklyor that the other bias voltages on the CRT are clamped to values that wouldblank the CRT once the set is off. If the problem developed suddenly, thenthis circuitry may have failed. On the other hand, if it has been graduallygetting more pronounced, then the characteristics of the CRT or othercircuitry may have changed with age. In most sets it is left to chance whether the picture tube capacitance willbe discharged by beam current at switch-off. It may simply be due to thebehaviour of the video control IC when its supply voltage drops that causesthe cathodes to be driven to white and this may not be formally specified bythe manufacturer of the IC. Some of of the latest sets have an explicitcircuit to discharge the EHT at shutdown. As noted in the section: "Safety guidelines" the HV charge on the CRTcapacitance can be present for a long time. A service technician shouldbe very aware of that before touching HV parts! Interestingly, most sets for the Asian Pacific market have a bleeder resistorbuilt in that will discharge the EHT without the need for a white flash atswitch-off. These will in fact drive the beam to black at switch-off via anegative voltage to the CRT G1 electrode. The AP market is very sensitiveto proper set behaviour, they don't like a white flash. In short, it all depends on the demands of the particular market, the chanceof the picture tube producing a spot/blob, and the mood of the designer. So, it may not be worth doing anything to 'fix' this unless the splotch isso bright (more so than normal video and for an extended time) thatCRT phosphor damage could result. This is usually not a problem withdirect view TVs but would definitely be a concern with high intensityprojection tubes. On the other hand, your phantom blob may provide for some interestingconversation at your next party! Disposing of dead TVs (CRTs and charged HV capacitors):------------------------------------------------------ I don't know what the law says, but for safety, here is my recommendation: Treat the CRT with respect - the implosion hazard should not be minimized.A large CRT will have over 10 tons of air pressure attempting to crush it.Wear eye protection whenever dealing with the CRT. Handle the CRT by thefront - not the neck or thin funnel shaped envelope. Don't just toss itin the garbage - it is a significant hazard. The vacuum can be safelyreleased (Let out? Sucked in? What does one do with an unwanted vacuum?)without spectacular effects by breaking the glass seal in the center of theCRT socket (may be hidden by the indexing plastic of the socket). Cover theentire CRT with a heavy blanket when doing this for additional protection.Once the vacuum is gone, it is just a big glass bottle though there may besome moderately hazardous materials in the phosphor coatings and of course,the glass and shadow mask will have many sharp edges if it is broken. In addition, there could be a nice surprise awaiting anyone disconnecting thehigh voltage wire - that CRT capacitance can hold a charge for quite a while.Since it is being scrapped, a screwdriver under the suction cap HV connectorshould suffice. The main power supply filter caps should have discharged on their ownafter any reasonable length of time (measured in terms of minutes, notdays or years). Of course around here, TVs are just tossed intact which is fortunatefor scavengers like me who would not be happy at all with pre-safed TVs! Shock and/or spark when connecting cable or other A/V components:---------------------------------------------------------------- TVs with hot chassis - where signal ground is actually line connected andat some intermediate (and dangerous) voltage - will have an isolation blockin between the tuner and antenna/cable connections. TVs with isolated powersupplies may have some bypass capacitors between the power supply and signalgrounds (including the A/V shields if there are A/V connectors). It ispossible for a failure to result in a serious safety hazard where the RF(antenna/cable) or A/V connectors become electrically live. However, a tingle or small spark might be normal. RFI bypass caps between theAC input and shield on the connector could result in some leakage - 50 V ormore might be indicated using a high impedance multimeter. This is harmless.Reversing the plug in the AC socket (if it is not polarized or if you are usingan unpolarized extension cord) might eliminate or greatly reduce the effect. Nonetheless, it should be checked out. Measure the resistance between eachside of the AC plug and the RF and AV connector shields. It should be 1 M ohmor more. Test for voltage between the cable (or other device) connector andearth ground. If there is anything significant, test the resistance on thedevice between its shield and its power plug as above - other devices may haveRFI bypass caps or be defective as well. What is the deal with Macrovision copy protection?:-------------------------------------------------- (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). JVC owns the patent for VHS. JVC has made a deal with Macrovision that from a certain date in the past *no* VHS recorder licenced by JVC shall be able to record any video signal that contains Macrovision's copy protection pulses. Any video recorder from before that date (VHS or other) mightwell work OK on the altered video signal ! The copy protection pulses upset the video-AGC and H-sync. TV's usually don't have a video-AGC.The stabilizer box removes the extra pulses and makes it into a normal video signal again. No VCR should ever know the difference, so they should all record properly again. At the same time, all TV's are required to ignore the copy protectionpulses. As a TV-designer I can tell you that this is sometimes far fromtrivial. Not in the least because in the beginning we were not includedin "the deal". There may be TV's around whose brightness and/or sync will be disturbed by the Macrovision pulses. Officially, this is the reasonfor existance of the stabilizer boxes: to view better, not to copy better.Unofficially, they are sold for copying, of course. The next step will be that digital-TV decoders will output an analog TVsignal with Macrovision copy-protection pulses so that you may watch but not record your pay-per-view program. Same problem, same solution ... And I thought that PAL/Secam/NTSC were *standards*, sigh ... Whether they like it or not (and from personal experience I can tell you thatwe don't like it) it is the responsibility of the TV set-maker (in your caseSony) to build a TV that takes the Macrovision copy protection pulses withoutshowing any side effects on the screen. Seems like they didn't do a good jobon your TV :-). But they will have to fix this, your complaint is valid. Ithink in this case it may be the dealer's responsibility too, maybe you cantrade it for a different brand ? And do try it out first ... Sadly, more complex TV's seem to suffer more than the simpler, old-fashioned,designs. Unfortunately, Macrovision seems to be satisfied when their pulsesdo not affect the majority of (mostly older) TV's. In your Sony TV, theclamping circuit seems to be affected by some ultra-black pulses in the signal.Maybe an anti-Macrovision decoder can help you, officially they are designedfor *this* purpose. AGC and copy protection:---------------------- (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). 1. RF-AGC which compensates for different signal strength at the aerial, it measures RF amplitude and is *not* sensitive to video contents because with negative modulation the sync is the peak and is constant, this AGC will not work on CVBS (baseband video) inputs. 2. Video-AGC which normalizes baseband signals which enter *after* the tuner-IF. A.o. this compensates for different signal strengths when you connect two VCRs together. It measures peak-white, so it *is* sensitive to video content and thus to the Macrovision pulses. And: a television does NOT have a video-AGC, unless you want to call the beamcurrent limiter circuits an AGC. (Exception: the Secam-L system with positivemodulation requires an RF-AGC which measures peak-white instead of peak-sync.) The RF-AGC does not see the peak-white of the anti-copy pulses.If you connect the VCR to the TV via the CVBS (baseband) input, thenthe RF-AGC is not even in the path. Still, it may be disturbed.But the sync separator may see the extra inserted Hsync pulses, anddue to the phase disturbance the video clamping may be disturbed too. On-screen clock runs slow or fast:--------------------------------- You will need the Sams' Photofact for the set. If the clock reference is power line derived, noisy power can sometimesresult in erratic timekeeping though running fast is probably more commonthan running slow. This could be a result of a lamp dimmer or compactfluorescent on the same circuit. If it has a separate crystal for the time keeping, that could be faulty. Now think about it: Do you absolutely need the TV's clock??? After all, thereare probably a half dozen other clocks in the same room! Cold problems with cold TVs - or - an unhappy Christmas:------------------------------------------------------- (From: Ren Tescher (ren@rap.ucar.edu)). My Christmas repair story wasn't so happy. I worked as TV repairman for an appliance store. On a very cold (20 below zero Fahrenheit) evening a man bought a new 25"console for the family. As we loaded it into the back of their pickup truck, we *told* them. "Do notplug this in until it warms back up to room temperature." They nodded andsaid "uh-huh, okay". They lived about 15 minutes away. 25 minutes later we get a telephone call... "Hey! that TV you sold us don't work!" So we ended up loading another TV into our delivery van, drove out to theirplace. Unloaded it, and WAITED until the thing was warm enough to plug in. Needless to say, I got home late that Christmas Eve and had brand new TVconsole waiting for my repair back at the shop. ******************* Some Model Specific Problems ******************* Erratic problems with older GE TVs:---------------------------------- Older GE TVs used double sided circuit boards with poor-man's vias - rivetssoldered to the traces top and bottom. These have been called 'Rivlets' and'Griplets'. Unfortunately, whoever did the design didn't realize that (1) thethe rivets did not heat adequately during soldering and (2) the expansioncoefficients of the rivets and circuit board were not qutie identical. Thus, erratic problems are almost a certainty with these TVs. Normal logicaltroubleshooting is useless. The only solution is to repair every !@#$ Gripleton all circuit boards in the TV. I have repaired these with a high power soldering gun used on both sides withliberal application of solder and flux. However, I do not recommend thisshortcut unless you are willing to redo the repair every couple of years. (From: Mr. Caldwell (jcaldwel@iquest.net)). There are two methods of repair. * Method 1: Clean the paint from around each griplet on both sides of the board to expose the surrounding copper pad. Apply liquid solder flux to the cleaned copper. Solder so as to bridge the griplet to the cleaned copper. * Method 2: Do the above but desolder the griplet and place a wire through it so that the wire extends beyond the griplet to the copper foil and solder the wire on both sides (this was the final fix GE used in this chassis). If done carefully Method 1 works and is reliable. I would normally do this prior to any troubleshooting, it repairs most problemsin this chassis. While you have the board out working on it be sure to alsoclean and resolder high temperature components and connections that look bad.These griplets can be on all boards, even the tuner control board. Erratic problems on late model GE, RCA, or ProScan TV:----------------------------------------------------- Problems with bad solder connections, mostly in and around the tuner are verycommon with several series of late model (e.g., CTC175/176/177 chassis)RCA/GE/Proscan TVs. Ignoring these erratic and intermittent problems can leadto serious damage including failure of the EEPROM and possibly other expensiveICs. Therefore, it is essential to deal with the solder connections as soonas these symptoms appear. The repairs are straightforward though perhapstedious. Thompson may reimburse for reasonable cost of repairs. Some of the common symptoms include: * Random power cycling. It may come on in the middle of the night! * Picture shifts or changes size vertically or horizontally. * Picture turns to snow or shows other reception problems. * Picture turns to random display of time or other data. * Noisy or muted sound, volume buttons have no effect. * Remote has no or unexpected effect. See the document: "RCA/GE CTC175/176/177 Tuner Repair" for additionalinformation on these types problems including repair procedures andapproaches to getting coverage from Thompson Electronics. Sylvania/Magnavox/Philips - no startup:-------------------------------------- Check the resistor supplying initial base current to the horizontal driver(not HOT) transistor. On many chassis, it is R502, 47 K. It opens for notgood reason. Why it fails is a mystery as its power rating should be adequate. Sony TVs/monitors and Hstat:--------------------------- Symptoms are that the TV or monitor will shut down possibly after a warmpupperiod. There can be other causes but failure of the Hstat module HV sensewire is quite likely on many Sony models. (From: Mr. Beanz (slin01@mail.orion.org)). If you've determined that the HV is fine, and the H-STAT is shuttingdown for no reason, it's possible to bypass. There is a little brownwire coming out the bottom of the H-STAT which goes to a 3-pinconnector. Two wires have a jumper, and the brown wire goes to theother. Snip the brown wire at the H-STAT and the TV will continue tofunction normally. Measuring the regulated B+ to the flyback will giveyou a pretty good indication of the condition of the HV output. If itremains steady at rated voltage (I forget what it was, 130V or 135V)then HV is A-OK. If it slowly creeps up or is too high to begin with,you have a problem. The voltage will normally jump to 150V or so afterHV shutdown is tripped. Ideally, you should replace the H-STAT in this case. Although takingthe poor man's route will WORK, you lose any protection in the eventthat the HV circuitry should malfunction. More on Hstat:------------- (From: Shawn Lin (slin01@mail.orion.org or lin@science.smsu.edu)). The H-STAT is a plastic box that sits mounted to the picture tube'sshield. It's red in color (for every SONY TV that I have owned) and hasa single knob on it. The flyback's HV output wire goes into the H-STATand another HV wire exists the H-STAT and connects to the anode cap onthe picture tube. It has a dual purpose, horizontal static convergence(the control adjusts this) and HV overvoltage shutdown protection. Chances are, your HV is within spec and the H-STAT is bad, but youshould make sure the regulated voltage to the flyback is steady anddoesn't fluctuate before assuming the H-STAT is bad. H-STAT is expensive, and may not be worth replacing. My KV-1952RS is old andas a whole, not worth the cost of a new H-STAT, so I just bypassed it anddidn't bother replacing it. The TV's been working great for over a year andthe picture is still excellent. Note: On some models, the sense wires need to be connected during startupor else it will never come on. CAUTION: On some monitors (like the Sony CPD1302), the sense signal may beused for actual HV regulation. Thus, if the sense wire is disconnected, (orthe divider inside the Hstat block fails open) there is no feedback and it ispossible for the high voltage (and probably B+) to increase until the HOT(and possible other components) blow. I do not know if this applies to Sonybuilt TVs as well. ******************* Items of Interest ******************* An informal history of X-ray protection:--------------------------------------- (The following is from: Marty). Most of the old tube type color TV sets used a shunt HV regulator tube,usually a 6BK4. If it failed, or some component in the HV circuit failed, thehigh voltage, normally 25KV, could go up to 35KV or more, causing some X-Ray leakage from the CRT. In the early 70s when news of this radiation scare was first announced, there was a public outcry to immediately fix the problem. The feds hastily imposed a requirement on manufacturers of TV sets to somehow render a TV set "unwatchable" if the HV exceeded rated limits. The manufacturers first response was to follow the letter of the law and the first "HEW" circuit simply blanked the video when the HV exceeded a setpoint to make the set "unwatchable". It was quickly noticed that the HV was not turned off with this circuit and the CRT still could emit some radiation. Many TV sets with this feature wereleft on so the consumer could listen to the sound, so the feds tightened the requirement. By this time new TV sets were all solid state and some manufacturersexperimented with HV shutdown circuits, but most of these circuits were poorly designed and not reliable. Zenith thought they had the answer by regulating the HV with a bank of 5 capacitors across the horizontal output transistor to "hold down" the HV to 25KV. If one capacitor opened, the HV would only rise about 2KV, not a dangerous situation. This wasn't good enough for the feds. The "fix" that Zenith finally came out with, was a "4 legged capacitor. Two legs were the emitter return for the horizontal output transistor, & two legs were the HV holddown capacitor (the equivalent value of the bank of 5 caps). This "fix" was accepted by HEW and millions of TVs were produced. It worked so well, that other manufacturers soon followed the lead (Magnavox, GE, etc.). Then the worst happened! The 4 legged monsters started failing in a large numbers. Not opening completely & not shorting out. They sometimes allowed the HV to skyrocket to over 50KV. Some of them even cut the necks off of the CRTs. Zenith issued a recall on those models with the problem (more than one entire model year). After several "improved" versions of the capacitor, the problem was fixed but that recall almost bankrupted the company. Other companies had failures too, but usually not as dramatic as Zenith's. Magnavox used the HV holddown capacitor, both single & 4 leg version in several 70s era TV sets and is a good candidate for fireworks as well. What is this goop around some electrolytic capacitors and other components?:--------------------------------------------------------------------------- That goop is probably glue and generally harmless - it is there to holddown the components aganst vibration. I have heard of it sometimesdecomposing and shorting stuff out but I doubt you have that problem. Therefore, unless you find a bad cap in the focus or related circuit, weare still looking at a flyback problem. What does the flyback (LOPT) transformer do?:-------------------------------------------- The typical flyback or Line OutPut Transformer (LOPT) consists of two parts: 1. A special transformer which in conjunction with the horizontal output transistor/deflection circuits boosts the B+ (120 V typical for a TV) of the low voltage power supply to the 20 to 30 KV for the CRT as well as provide various secondary lower voltages for other circuits. A HV rectifier turns the high voltage pulses into DC and the CRT capacitance smooths it. The HV may be developed from a single winding with many many turns of wire or a lower voltage winding and a diode-capacitor voltage multiplier. The various secondary voltages power the logic, tuner, video signal, vertical deflection circuits, and CRT filament. In fact, with many TV designs, the only power not derived from the flyback is for the keep-alive circuitry needed to maintain channel memory and provide startup drive to the horizontal deflection/high voltage system. 2. A voltage divider that provides the focus and screen supplies. The pots are in this divider network - and these things fail resulting poor focus, uncontrolled brightness, or fluctuating focus and/or brightness. A total short could also result in failure of other components like the horizontal output transistor. In some TVs, the focus and screen divider and/or controls are external to the flyback and susceptible to dust and problems particularly on humid days. The resistance of these circuits is so high that dirt or other contamination can easily provide a bypass path to ground especially when slightly damp. Why do flyback (LOPT) transformers fail?:---------------------------------------- While flyback transformers can on occasion be blown due to a failure elsewherein the TV or monitor's power supply or deflection circuits, in most cases,they simply expire on their own. Why? Flybacks are wound with many layers of really really fine wire with reallyreally thin insulation. This entire assembly is potted with an Epoxy resinwhich is poured in and allowed to cure. In some ways, these are just short circuits waiting to happen. Flybacks get hot during use and this leads to deterioration of the insulation.Any imperfections, nicks, scratches, etc. in the insulation contributes tofailure. Temperature cycles and manufacturing defects result in fine cracksin the Epoxy potting material reducing the insulation breakdown particularlyin the area of the high voltage windings, rectifiers, and focus/screen dividernetwork. It is amazing they last as long as they do with the stress they are under.They also physically vibrate to some extent. A whole bunch of other factorsare also no doubt important. Brief comments on testing the HOT:--------------------------------- For a TV with no blown fuses that will not start, here are two quickychecks to see if the HOT is good and has power and drive: * HOT tests - check across each pair of pins for shorts (preferably removed from the circuit board). No junction should measure less than 50 ohms or so. Lower readings almost certainly indicate a bad HOT. If in-circuit, however, the reading between base and emitter will be near zero due to the secondary of the driver transformer. See the document: "Testing Diodes and Bipolar Transistors with a DMM or VOM". Don't be confused by internal damper diodes and B-E resistors. * Power - measure across the collector to emitter with a multimeter (with the HOT removed or if there is no deflection, this is safe with it in place). There should be solid B+ - typically about 100 to 160 V (115 VAC sets - possibly higher for 220 VAC sets). If this is missing, iether there is a problem with the power supply or the emitter fusable resistor has blown (probably in addition to the HOT) and there is no return. * Drive: put an oscilloscope on the base - there should be pulses around .7 V for most of the scan (~50 microseconds) and probably going negative a couple volts at least for retrace (~12 microseconds). If drive is weak or missing, determine how startup is implemented as there may be a problem in the startup power supply or deflection IC. WARNING: use an isolation transformer for the oscilloscope tests (and wheneveryou are probing a TV in general)!!! This part of the circuit, in particular,is usually line connected. See the sections on safety. CRT rejuvenation:---------------- Where one or more electron guns in the CRT have deteriorated due to wear andtear, it is sometimes possible to give them a new, but possibly, temporarylease on life through rejuvenation using a special piece of CRT serviceequipment. (From: Gary Klechowitz (klechowi@execpc.com)). When I rejuvenate a tube I inform the customer that there is no warranty onthe job. Rejuvenating a CRT is like when Clatuu was brought back to life byGort in "The Day The Earth Stood Still". When asked "How long will you live"?he replied: "no one knows". I use a Sencore Beam Builder. If your tube is just moderately dim and blurrybut still shows good cut off threshold, I would just use the auto restore modeon the beam builder rather than using the restore button. If the tube isreally bad with little or no cutoff threshold, then the rejuvenator is neededbut that has less than a 50% chance of fixing the tube and in many cases thetube gets worse to trashed in the process. Memory chips in TVs:------------------- (From: Mark Zenier (mzenier@eskimo.com or mzenier@netcom.com)). Actually, they are EEPROMs. A modern TV has integrated the circuitryso that the microprocessor that controls it also sets the variousadjustments like vertical height and other characteristics. The samememory that knows what channels are valid and what the brightness andother user adjustable settings are is used for factory adjustments thatare set when the TV is first turned on. It's a lot cheaper to use theremote control signals that are already there than add a handful oftrimmer resistors. For service purposes there is often a magic key sequence used with yourremote control to access a service page in the on screen display thancan change these. Since you can easily set something that could fry thevarious high power deflection circuits, getting a little too curious canvoid your warranty, and toast your set. How does Picture-In-Picture (PIP) work?:--------------------------------------- A separate video input or tuner provides the PIP baseband signal which is thenresized and stored in a frame buffer large enough to hold the X and Ydimensions of the PIP image. Readout is timed to place the PIP image in theselected area of the screen and it is substituted for the main video. Whatcould be simpler?! Tony's notes on setting convergence on delta gun CRTs:----------------------------------------------------- (This section from: ard12@eng.cam.ac.uk (A.R. Duell)) The older delta-gun tubes (3 guns in a triangle, not in a line) can give **excellent** pictures, with very good convergence, provided: 1. You've set those 20-or-so presets correctly - a right pain as they interact to some extent. 2. The CRT is set up in the final position - this type of tube is more sensitive to external fields than the PIL type. Both my delta-gun sets (a B&O 3200 chassis and a Barco CDCT2/51) have very clearly set out and labeled convergence panels, and you don't need a service manual to do them. The instructions in the Barco manual are something like: "Apply crosshatch, and adjust the controls on the convergence board in the numbered order to converge the picture. The diagrams by each control show the effect". Here's a very quick guide to delta gun convergence where the settings aredone using various adjustments on the neck of the CRT (if you don't have a service manual but do know what each control does, and where they all are -otherwise, follow the instructions in the service manual --- sam): 1. Apply a white crosshatch or dot pattern to the set. Don't try and converge on anything else - you'll go insane. It's useful to be able to switch between those 2 patterns. 2. Before you start, set the height, width, linearity, pincushion, etc. They will interact with the convergence. Also check PSU voltages, and the EHT voltage if it's adjustable. That's where you do need a service manual, I guess. 3. Turn off the blue gun using the A1 switch, and use the red and green static radial controls to get a yellow crosshatch in the middle of the screen. These controls may be electrical presets, or may be movable magnets on the radial convergence yoke (the Y-shaped think behind the deflection yoke). 4. Turn on the blue gun and use the 2 blue static controls (radial and lateral) to align the blue and yellow crosshatches at the center of the screen. Some manufacturers recommend turning off the green gun when doing this, and aligning red with blue (using *only* the blue controls, of course), but I prefer to align blue with yellow, as it gives a check on the overall convergence of the tube. 5. Turn off the blue gun again. Now the fun starts - dynamic convergence. The first adjustments align the red and green crosshatches near the edges - I normally do the top and bottom first. There will be 2 controls for this, either a top and a bottom, or a shift and a linearity. The second type is a *pain* to do, as it's not uncommon for it to affect the static convergence. 6. Getting the red and green verticals aligned near the edges is a similar process. 7. You now have (hopefully) a yellow crosshatch over the entire screen. 8. Now to align the blue. This is a lot worse, although the principle is the same. Turn on the blue gun again, and check the static (center) convergence 9. To align the blue lines with the yellow ones, you'll find not only shift controls, but also slope controls. Use the shift controls to align the centers of the lines and the slope controls to get the endpoints right. These interact to some extent. You'll need to fiddle with the controls for a bit to work out what they do, even if you have the manual. The convergence over the entire screen should now be good.... A word of warning here... The purity is set by ring magnets on almost all colour CRTs, but on PIL tubes, there are other ring magnets as well - like static convergence. Make sure you know what you are adjusting. Saga and general setup for large CRT TVs:---------------------------------------- (Responses from: Tony (ard12@eng.cam.ac.uk), panic from V.K.) > I'm having problem(s) with a brand new 40" Mitsubishi tube (direct> view) TV. I'm writing this with hopes of getting some basic information > so that the dealer doesn't bamboozle me. > From first viewing (5 minutes after the delivery man departed). I noticed a> discoloration patch in the top right hand corner (purple when the> background is blue/greenish when background is white). As you probably know, a colour TV produces a red picture, a green picture and a blue picture on the screen at the same time. You eyes interpret that as a coloured picture. If you look at (a normal, non-projection) TV screen through a magnifying lens, you should be able to see red, green and blue dots, and no other colours. Now, there are 3 basic adjustments to getting a good colour picture : 1. Purity. This means that the red picture is only red, the green picture only green, etc. This is the one that needs setting up on your set - you have a purity problem 2. Convergence. This means that the 3 pictures line up over the entire screen (or as much of it as possible). If this one is wrong, you'll see coloured fringes around objects in the picture. 3. Grey scale. This sets the overall colour of the picture - it means that white is really white, etc. It varies the relative intensities of the red, green and blue pictures. > I called the store in a panic and they calmly told me to> press the "degauss" button to eliminate the problem (which I> quickly learned was spurious magnetization, caused perhaps by> storage near a speaker in the warehouse?). Result? Better> but not cured. Yes, spurious magnetization (or more correctly a different magnetic field around the tube from the one present when it was set up) will cause purity problems. > The next day I visited the store, and the manager said (again) that> this was an easily fixable problem, requiring a few waves of> a degaussing coil. To appease me, he sends the salesman home> with me with small (1 foot diameter) coil in tow. Salesman (boy,> actually) waves the coil in front of and around set but can't seem to> remove the discoloration. Argh... Here's what should have been done IMHO. 1. The set should have been degaussed (a fancy word for demagnetized). 2. They should have connected a 'pattern generator' to the set. This is a piece of equipment that generates various test signals. They should have selected 'red raster' (which will appear to you as a pure red screen), and set up the purity adjustments on that. You should ask to see the pure red raster (and pure green and pure blue if the generator will allow it), and make sure there are no strange-coloured patches. If you like, you can examine the screen through a magnifying lens to check that there are no dots of other colours appearing - I do that when I'm setting up a new TV or monitor. 3. They should then have displayed a 'cross hatch' on the screen. This is a grid of white vertical and horizontal lines. Convergence errors are shown by the lines splitting into 2 or more colours (normally one of the 'primary colours' - red, green, or blue, and its complementary colour (cyan, magenta, and yellow)). Note, however, that it's _very_ difficult or even impossible to get perfect convergence over the entire screen on a modern tube, and that you'll not notice small errors near the corners on a TV screen. Note that some engineers prefer to set up the convergence on some other type of display (dots, for example), but you should at least be able to see a cross hatch pattern (all pattern generators provide that one) 4. They should have then displayed a 'grey scale' test display. This is a pattern of vertical grey bars of different brightnesses, from black to white. They should all have been a neutral grey, without colouration. Note that convergence and purity interact to some extent, and thus if either is adjusted, both must be checked (and rechecked). Grey scale adjustments interact with nothing else. I would want to see the set on a pattern generator (at least the patterns I've mentioned above) and identify the problems. > To demagnetize the TV, he says that a large coil is required, that> encompasses the whole unit; service rep will 'be in touch'. I've never heard of that - the correct procedure is to wipe the coil around the front, top, sides and bottom _NOT the back_ and then move it 2-3m from the set before turning it off. It doesn't matter whether the set is on or off for this, btw. I've not heard of putting a large coil round the entire set. (See the section: "Degaussing (demagnetizing) a CRT"). > After the sales boy leaves, I could SWEAR that the picture quality> in general is decreased, with people (especially their extremities like> lips and ears) appearing pinker than before, and also more general> interference (fringes/noise) noticeable. The convergence and purity are set by ring magnets on the neck of the tube. It's possible that the degaussing procedure has slightly demagnetized these, and if so, the whole set will need to be set up. Similarly, if any part of the set was magnetized at the factory, then the adjustments may have been set up to compensate, and then after demagnetization, they'll need to be reset. > So my questions are these. Can the original problem truly be FIXED> with proper sized coil and application? I don't think the size of the coil will make any difference. I would want tosee that set on a pattern generator, so I could be _sure_ as to what the problems are. If the dealers don't have a pattern generator, then they're not fit to be fixing TVs IMHO. > Could I be imagining that the waving of the small coil degraded the> picture quality? It's possible, but fairly unlikely. See above > Should I demand replacement to a new set? Can I legally ask for> this, or is it like a new car...you own it, now you deal with> the service guys forever. I don't know US law, but in the UK, if a product is defective, you candemand a refund of the money paid (not a replacement or a repair, a refund).IMHO, a TV with incorrect colours is defective... Liquid coupling fluid for projection TVs:---------------------------------------- (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). The liquid serves two purposes: 1. It conducts the heat away from the surface of the tiny picture tube. 2. It couples the light from the glass surface of the picture tube to the glass surface of the projection lens. Using air instead of liquid would give too much unwanted refraction at the glass-air interfaces I believe that the composition of the liquid is mostly water + glycol,quite similar to the anti-freeze liquid in your car's radiator, butwithout the colorants added that should warn you against drinking it. A good replacement kit contains not only a plastic bottle of liquidbut also new rubber sealing rings to keep it in, where it belongs.It's always recommended to buy the original stuff, if you can find it. (From: markmtf@earthlink.net). I just wanted to throw my $.02 in since I was one of the original members ofthe design team for the first Magnavox and Sylvania PTVs. I don't recall the models, but essentially, there are several generationsof liquid cooled/coupled PTV designs. One type consists of a set of CRTs witha liquid cell as part of that component. The other type consists of a liquidcell that directly couples the CRT faceplate to the lens. The liquid is a solution of DI (deionized) water and propylene glycol,with a small amount of surfactant to eliminate bubbles sticking to theglass and plastic surface. Distilled water can be used. The propyleneglycol is USP grade, not commercial grade for clarity reasons. You need toorder this through a lab supply company and specify USP grade. If you usea cheaper grade, the solution may become cloudy. The mixture of yoursolution should be somewhere between 50/50 to 80/20 water/glycol. The aremany kinds of surfactant which can cause cloudiness or foaming. You shouldprobably leave this step out if you are just adding rather than replacingliquid. If you want to experiment, you might try some fluid from aphotographer darkroom supply store that is used for eliminating watermarks during the film drying process. Just add a few drops to 1/2 liter.Then heat it up to check for cloudiness. If it works, then you are inbusiness. Again, if you are careful with filling the cell so that youdon't mix in air, you probably don't need any surfactant. I probably can't help you too much on the seals or gaskets. It is verydependent on the specific model. Both types of liquid cells loose theliquid over time due to vapor traveling through the silicone seals. TheCRTs with the cooling cell used a special RTV for a seal. The CRT/Lenscooling cell used silicone gaskets. There is a tradeoff on how tightly thegaskets can be tightened down due to CRT specifications. Somemanufacturers were also working on a expandable chamber to reduce buildupof pressure when the liquid expanded due to heat. The higher the pressure,the faster the liquid would evaporate through the gaskets. Comments on color purity, set orientation, and doming:----------------------------------------------------- "The problem with my TV is that bright parts of the picture change color. For example, white areas may shift towards yellow or blue depending on the orientation of the set. What are the possible causes of doming? I have noticed that the magnitude of the doming effect varies with TV orientation even after degaussing several times at the new orientation. Does this help identify the cause of the doming in my case?" (Portions from: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). The problem with regular shadow masks is 'doming'. Due to the inherentprinciple of shadow masks, 2/3 or more of all beam energy is dissipatedin the mask. Where static bright objects are displayed, it heats up severalhundred degrees. This causes thermal expansion, with local warping of themask. The holes in the mask move to a different place and the projectionsof the electron beams will land on the wrong colours: purity errors.The use of invar allows about 3 times more beam current for the samepurity errors. Both local doming and magnetic fields compete for the remaining landingreserve. Due to improper degaussing, the doming problem may be more visible.And applying a tube designed for the wrong hemisphere may very well increasethe doming complaints. It is possible to deliberately offset the nominallanding in order to get more doming reserve (the shift due to doming isalways to the outside of the tube). You would do this using spoiler magnetsput in the right places. Permanently setting the contrast lower is not a real cure because the customermight not like such a dark picture. A better picture tube (Invar shadow mask)*is* a good cure (in most cases) but there is the cost price increase. (Thisis mainly due to the fact that Invar metal is harder to etch.) Also see the section: "Comments on color purity, set orientation, and doming". About instant-on TVs:-------------------- Most TVs built since, say, 1980 have only the microcontrollerpowered from a small transformer when the set is off. This permits theremote control or front panel pushbutton to switch the set on. This circuitryshould be no more prone to catastrophic failure than what is in a VCR ordigital clock. Historically, there were 'instant on' TVs which kept a substantial portionof their circuitry live all the time - especially those using vacuum tubesin at least part of the circuitry (other than the CRT). In these, therewas a lot more to fail. Those tubes would continue to change theircharacteristics for many minutes when warming up. Circuits were also much moretouchy - remember all that constant tweaking! Thus, it made sense fromthe users's perspective to eliminate the warmup period and keep those tubestoasty all the time. In modern solid state TVs, the only component to really need a warmup periodis the CRT. All this means is that you have to wait 20 seconds forthe picture to appear. About gadgets to use house wiring as TV antenna:----------------------------------------------- Note that these $10 devices usually contain a single 5 cent ceramic capacitoras their 'sophisticated electronic circuitry'. The rest of the fancy plasticcase is just for show. (The following is from: Greg Smith (LiveTV@en.com)). Most people mistakening believe that the larger the antenna the betterthe received signal. The truth of the matter is that each element ofthe antenna must be cut to a precise length depending upon thefrequency of the signal you are attempting to receive. Further more,each element must also be spaced a precise distance away from theothers. This creates what is commonly called a "directional array".(see diagram below) By providing enhanced reception (gain) in thedirection the antenna is pointed, it also provides decreased receptionfrom the sides and back. (directivity) This prevents "ghosting" whichis caused by the same signal arriving at the TV at a slightlydifferent time because the signal bounced off of some structure onit's way to your set. If you use the house wiring as the antenna, the length will be randomand the orientation to the received signal will also be random.Therefore it will pickup the bounced/reflected signals just as well asthe primary signal. IE: lots of ghosting = very poor picture quality. Any kind of directional antenna, even a small one, whether inside oroutside, should provide a superior quality picture to that from thedevice you are talking about. Even a cheap "rabbit ear" antennamounted on top of the set allows you to orient it in the bestdirection. If you only receive the VHF channels (2-10) in your area then buy aVHF ony antenna. If you only receive the UHF (19-60+) then buy a UHFonly. If you get some of each then make sure that it is a combinationantenna. If your set has separate inputs for VHF/UHF make sure youalso get one with the proper splitter. ------------------- ------()------- -------- ---- ^ direction of signal Can I add an S-Video input to my TV or VCR?:------------------------------------------- Possibly, but why bother? You will most likely be limited by the TV or VCR'scircuitry anyhow. All S-Video means is (1) a special connector and (2) separate luminance (Y) andchrominance (C) rather than composite video. In a VCR, you will need to bypass the input circuitry and get to the placewhere Y and C are separate. This may or may not be possible depending on itsdesign. In a TV, they may never be separate and you will need to substitute your owncircuitry for the chroma demodulator. It is probably not worth it as you will likely not gain much in picture qualitybut if you really are determined, a schematic will be essential in either case. If all you want to do is allow for an S-video input, there are single chipswhich will combine the Y and C into a normal composite video signal. Also, see the section: "How do I add A/V inputs or outputs to a TV which doesnot have them built in?" since there may be safety implications in the case ofadding S-Video to a TV without any A/V jacks. How do I add A/V inputs or outputs to a TV which does not have them built in?:----------------------------------------------------------------------------- For A/V inputs (video and audio) The place to do this is after the videoand audio IF where baseband signals are normally separate. For audio, in particular, an alternative is to tap into the audio circuitrywhich may be elsewhere. Even the loudspeaker outputs can be used but thenwithout additional switching, you cannot disable the internal speakers whenyou are using your stereo system. Depending on the model of TV, doing any of this may be trivial to impossible -or a serious safety hazard. * Trivial: many low-end models use the same chassis (read this: circuit board) as the high end A/V receivers. Either there will be some parts missing, a cable connection to the missing A/V panel, or a missing auxiliary board which would have the A/V interface and jacks. If this is the case with your model, then it should be straightforward and safe to tap into the circuits at that point. A service manual or Sams' Photofact for the set will probably even identify the additional circuitry present in the higher priced models with A/V inputs. If, on the other hand, everything is crammed onto a single circuit board with no evidence of A/V signals, it may be very difficult as suitable tap-in points may simply not be available. * Hazardous: many TVs have circuitry which is not isolated from the AC line. If this is the case with your set, then it may be more trouble than it is worth to provide the essential isolation barrier between the TV and your external A/V equipment. The only 'easy' solution for audio at least is to include an isolation transformer RATED FOR LINE VOLTAGE ISOLATION in each signal path to the outside world. A means of isolation can be provided for video as well but it has to be able to handle the 6 MHz or so bandwidth of the video signal. A simple capacitor even if rated for sufficient voltage will probably not work and could be hazardous since it would need to have a high uF value to pass the lower frequency end of the video signal. If what you are really after is replacing a dead tuner/IF with your own tuneror converter, this may be possible but, again, may not be worth the trouble.The antenna isolation circuitry is probably external to the TV's tuner soyours could be substituted in its place. Of course, any user contact with thetransplanted device would then have to be TOTALLY prevented since a seriousshock hazard would be present for all metal parts and connections includingshield grounds. In addition, many components would likely blow the instantpower was applied if this were not done perfectly. Unless you intend to always use the direct A/V inputs and forgo the tuner,you will need some way of selecting between them - a switch or relay.This could be manual - you push a button or flip a switch - or automatic.There are all kinds of ways to doing the detection - mechanical, checkingfor a low impedance connection, looking for a signal, using a switch, etc. You will need a schematic - don't attempt this without one (for safety, ifno other reason). Even some TVs that have A/V jacks use a live chassis andprovide isolation for each signal (though this is the exception rather thanthe rule). So, even adding another A/V jacks to one of these would behazardous! Adding variable volume headphones to a TV:----------------------------------------- "My Mother-in-Law is hard of hearing. He is not. Is there such a thing as a variable volume headset that can hooked up while maintaining normal volume on the main speakers?" Greetings. But of course... The cost is $9-ish per set and it includes a 9foot (yup, 9 foot) cable and a handy, in-line volume control. The setuprequires an audio output somewhere on the TV itself - is there a headphonesjack? If yes, all you need is a "Y" (splitter) and two sets of headphones.If not, hmmm.... Either you or the local TV repair shop will need to add one.Depending on the circuitry of the speaker amplifier inside the TV, this maybe as easy as splicing in a headphone jack and drilling a hole for it on thecase, or as hard as somehow matching the impedance of the speaker to that ofthe headphones. You *will* need to look at the schematic or measure thespeaker/signal. See the section: "How do I add A/V inputs or outputs to aTV which does not have them built in?" for the very important safety issues. First, however, make sure they have a TV with a headphones jack or have oneput in (or get a TV that *does* have one). The 'Y' adapter can be purchased inany Radio Shack. Any cheapo one will do - no need for gold plating (they willtry to sell it to you ;-) should be under $5. Building a Frankenstein TV:-------------------------- Here is an interesting questions: "I got a lot of partially gutted TVs at an auction (All the same brand) and I'm trying to build a 'Frankenstein TV'. I have a 13" unit with a working power supply board and tuner board in one set. I have another set with a 25" picture tube in it. I'd like to drive the big tube with the guts from the small TV. Does anyone know If I'll blow up my workbench if I attempt this sort of transplant?" It won't blow up your workbench but the differences are probably significantenough that the performance would be unsatisfactory if it worked at all. In addition, this may blow up the power supply board - kill the horizontaloutput transistor and/or low voltage power supply itself - as the requiredpower levels are higher. If you have nothing to lose, power your Frankensteininitially through a series 100 W light bulb and Variac. Then you will be ableto tell if you are even close with less risk of blowing expensive parts. Of course, this does assume that all the organs your are merging are actuallygood to start with. Why do you you think they unloaded those TV carcasses? While the same chassis may be used for 19" and 25" sets, going from 13" to25" is likely to have many differences. Turning a TV (or monitor) into an oscilloscope?:----------------------------------------------- This question comes up so often and it does sound like a neat project togive a defunct TV a second life. Don't expect to end up with a Tek 465on the cheap when you are done. However, it could be a fun learningexperience. CAUTION: See the safety recommendations below. You will be severely limited in the performance of such a scope. TVs andmonitors are designed to operate at a very narrow range of horizontal scanrates and the high voltage is usually derived from the horizontal deflection.So, you would need to retain the original deflection system for this purposeat least. 1. You will need to disconnect the deflection yoke from the horizontal and vertical deflection circuits of the TV or monitor without killing the HV. (also, doing all this without killing yourself as well). Depending on the design, this may be as simple as unplugging the yoke connector. More than likely, you will need to substitute a load for the horizontal deflection coil. A coil from another sacrificial similar TV or monitor would probably suffice. Warning: at this point you have a really bright spot in the middle of thescreen which will turn to a really black spot if the brightness is not turnedway down really really quickly. 2. For the horizontal, you need a ramped current source. You are driving a non-ideal inductor (the deflection coil) so it has both inductance and resistance. Thus the waveform is a trapezoid - a voltage ramp (for the resistive part) superimposed on a voltage step (for the inductive part). This should not be too difficult. Don't expect to be able to achieve really fast sweep. Even running at normal TV rates is non-trivial. 3. Similarly, for the vertical you need to drive with a voltage (your signal) controlled current source. However, if you are just screwing around, then the linearity etc. for the vertical may not be that important. In this case, one way is to put a current sensing resistor in series with the deflection coil and use this in a power op amp type of feedback arrangement. (You could do this for (2) as well. 4. There is a good chance that the original brightness control will work as an intensity adjustment. However, with some TVs and monitors, this depends on receiving a valid video signal. You may need to improvise. If you do want to control the intensity from a signal source, you should be able to tap into the drive signals going to the little board on the neck of the CRT. 5. Don't expect high bandwidth, uniform response, or any of the other things you take for granted with a decent scope. That takes work. However, as a fun project, this certainly qualifies. Interchanging the functions of the horizontal and vertical deflection yoke (and rotating it 90 degrees) may provide a better match of horizontal and vertical bandwidth to your intended applications or experiments. 6. With a color TV or monitor, these experiments could be quite interesting and educational but there may be color fringing effects since you are not compensating for certain aspects of dynamic convergence at all. 7. SAFETY: Once you disconnect the deflection yoke from the TV or monitor's circuits, move the original circuits out of the way and put a barrier between between you and the rest of the TV or monitor. All you will need are connections to the deflection yoke on the CRT (unless you want to do intensity modulation in which case you will need to drive the video output(s) to the CRT cathodes. I would recommend against doing this if your unit is one of those with a totally 'live' chassis as there would be additional safety hazards and circuit complications). (From: Chris Crochet (ccrochet@premier.net)). Hehehe... Actually, I've done this one :) I've got two old IBM mainframe terminals, painted like charred metal,hooked up to each channel of the 'B' speaker outputs on my stereo. It'sstrange looking and always an attention getter when I have guests. Notto mention, the long-persistence phosphor they use makes interestingtracers :) One caveat, at least on these monitors (I don't know what other monitorsthis might apply to). When you turn them off, the circuitry shuts downin the following order: horizontal drive first, electron gun second, andvertical drive last. Therefore, if there is no vertical deflection,which would be the case if the stereo is quiet, the active electron beambecomes perfectly stationary during the course of shutdown, thus burninga hole in the phosphor. Oops :) I found it more effective to hook thestereo into the HORIZONTAL drive, thus avoiding this problem. Not quitelike your average oscilloscope. Another interesting effect -- if the electron gun is active duringvertical blanking interval, it seems to deflect so far that it bouncesoff the SIDES of the picture tube, and sprays all over the phosphor,making some interesting images. (From: Lance Edmonds (lanceedmonds@xtra.co.nz). Some years ago ELEKTOR and Electronics Australia magazines published articleson a design for this. Dick Smith Electronics in both NZ & Australia used tosell the kit. Max Bandwidth was a startling 10 or 15Khz. Enough for elementary audioservicing. Those magazines also published designs for delayed sweep & trigger modules asadditions to any basic 'scope. Plus, a storage scope design, logic analyzerdesign, and a Dual trace emulator design. Enough to keep the average hobbist/experimenter happy for quite a while (g). (From: Dale H. Cook (dhcook@rev.net)). Every few months someone will pop up with this question. A TV would not make avery good scope. Bandwidth would be limited and the amount of work needed tobuild the horizontal and vertical amplifiers, sweep and triggering circuitsand so on wouldn't be worth the effort. You'd need even more work to addmodern features such as delayed triggering and variable hold-off. Don't eventhink about multiple channels and the advantages they offer. In a time when Isee used Tek 465s offered for $200 it certainly doesn't pay to try to converta TV. If you are just looking for a challenging electronic project I can thinkof several that have a far better chance of yielding something useful. Now,if you were starting with an antique set that used an electrostatic CRT youmight do a bit better, but a 1937 Dumont will set you back about $3,000.00 orso - a little too much of an investment. (From: Tony Duell (ard@p850ug1.demon.co.uk)). I've worked on the vector monitors that were used on some of the 1970's minicomputers. These are essentially X-Y displays (not raster scanned), andwould make audio-bandwidth 'scopes if given a timebase. I would guess at abandwidth of the order of 100kHz. Some of them (DEC, certainly, maybe Tektronix) were electromagnetically deflected like a TV. However, there are a couple of things to be aware of.Firstly, the output amplifier, which drives the yoke at constant current, ispretty complex. Secondly, the yoke is specially made - the 2 sets of coils arepretty similar (unlike those in a TV), and the inductance is critical. So, while I'll keep these monitors running, I'd not want to have to covert aTV into one :-). (From: David Katz (DAVEKATZ@prodigy.net)). If by chance what you want is an X-Y display for audio, not a (more typical)X-T, it's easy. Just put a resistor in series with each yoke (about 100 ohms,5 W) and drive them with a stereo amp. (From: Steve Roberts (osteven@akrobiz.com)). Your best hope might be to get a older generation heart monitor from ahospital, these have a professional X-Y display module to begin with, andare surprisingly easy to hack, mine was $10 at the local surplus shop. Theultra long persistence phosphor is a pain/blessing depending on what youare doing. Displaying a video signal as a picture on an oscilloscope:--------------------------------------------------------- I am not sure why anyone would really want to do this other than as anexperiment - it would be interesting one. If a composite video signal is the input, you will need a sync separator. You will have to construct a vertical deflection voltage ramp generatorwhich can be locked to your vertical sync signal. The horizontal timebase of the scope will be fine for the horizontaldeflection and should easily lock to your horizontal sync pulse or(if the scope has a TV trigger mode) directly to the video signal. A video amplifier will be needed if your Z axis does not have an internalamplifier (you need .7 V p-p to be full brightness range.) Unless you provideautomatic gain control, this will need to include offset (brightness)and gain (contrast) adjustments. Even if there is an internal amplifier, itmay not have the required bandwidth for the video signal. However, the overall brightness may be disappointing - a scope is not designedfor overall high brightness. The beam focus will not be as good as that ona little TV either. Use of surge suppressors and line filters:----------------------------------------- Should you always use a surge suppressor outlet strip or line circuit?Sure, it shouldn't hurt. Just don't depend on these to provide protectionunder all circumstances. Some are better than others and the marketingblurb is at best of little help in making an informed selection. Productliterature - unless it is backed up by testing from a reputable lab - isusually pretty useless and often confusing. Line filters can also be useful if power in you area is noisy or proneto spikes or dips. However, keep in mind that most well designed electronic equipmentalready includes both surge suppressors like MOVs as well as L-Cline filters. More is not necessarily better but may move the pointof failure to a readily accessible outlet strip rather than the innardsof your equipment if damage occurs. Very effective protection is possible through the use of a UPS (UninterruptiblePower Supply) which always runs the equipment off its battery from the internalinverter (not all do). This provides very effective isolation power lineproblems as the battery acts as a huge capacitor. If something is damaged,it will likely be the UPS and not your expensive equipment. Another optionis to use a constant voltage transformer (SOLA) which provides voltageregulation, line conditioning, and isolation from power spikes and surges. It is still best to unplug everything if the air raid sirens go off oryou see an elephant wearing thick glasses running through the neighborhood(or an impending lightning storm). GFCI tripping with TV, monitor, or other high tech equipment:------------------------------------------------------------ Ground Fault Circuit Interrupters (GFCIs) are very important forminimizing shock hazards in kitchens, bathrooms, outdoors and otherpotentially wet areas. They are now generally required by the NEC Codein these locations. However, what the GFCI detects to protect people - animbalance in the currents in the Hot and Neutral wires caused possiblyby someone touching a live conductor - may exist safely by design inhigh tech electronic equipment. The result - false tripping - ismostly a problem with 3 wire grounded devices with built in line filtershaving capacitors between Hot and Ground but may also occur with 2 wireungrounded TVs due to the power-on surge into the highly capacitiveor inductive loads of their power supplies. Multisystem TVs:--------------- The question often arise: can my NTSC TV modified to display PAL signals(or vice-versa). Unlike a VCR where there are substantial differencesbetween recording of NTSC and PAL, the problem of displaying the pictureis much simpler. The following assumes 525 line NTSC and 625 line PAL: The horizontal scan rates are nearly identical (15,734 Hz for NTSC and15,625 Hz for PAL), so this is not likely to be a problem. If thesediffered significantly, then there would be design issues similar tothose for multisync computer monitors and this would drive up cost. The vertical scan are slightly more of a problem with 525 line/60 HzNTSC and 625 line/50 Hz PAL. But it is a lot easier to design verticaldeflection to accommodate a modest variation in rates. TVs could be easilydesigned or modified to accept either. The color encoding techniques differ but inexpensive ICs exist thatcan deal with either standard. In fact, many are programmable todo either with a jumper and slight modifications to the externalcomponents. Displaying a monochrome - B/W - picture on the other kind ofset is usually possible if the set has a vertical hold controlor enough vertical range. Modifying the chroma circuitry ismore complicated but it should be possible to substitute asecond IC and patch it into the existing video chain. As far as commercial multisystem TVs are concerned, the real reason wedo not see many of these (at least in the U.S.) is lack of demand. Theyare available if you look hard enough and are willing to pay a premium.They are readily available on the international market. Playing NTSC videotape on a PAL TV:---------------------------------- "Does anyone know if NTSC VCRs (NTSC is a special feature in Ireland) require an NTSC capable television too, or can they convert NTSC signals to PAL (seems unlikely)?" (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). There are 4 possible answers: 1. The VCR does not convert an NTSC signal to PAL, it outputs pure NTSC and you need an NTSC-compatible TV to view it. 2. The VCR converts NTSC 3.58 to NTSC 4.43 and you need a PAL-TV adapted to NTSC 4.43 to view it (relatively minor adaptation). 3. The VCR converts NTSC 3.58 to PAL 4.43 but keeps the field rate at 60 Hz. That is definitely not a standard signal! Some standard PAL-TV's will permit viewing it, and some Won't! At least be prepared to see interesting artifacts and crosstalks. 4. Conversion to real standard PAL is very expensive, thus unlikely. The most likely answers are 1 and 3, check the spec of the VCR. The NTSC 4.43system has been sold to middle-east and maybe US-military. Buying a TV in Europe:--------------------- "I have the following question for you specialists: Can I buy a TV in any west-european country and use it in any other west-european country? For example, buying a TV in the Netherlands and use it in Greece or buying in France and using in England." (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). The general answer is: NO. There are multi-standard TV's that cover more countries, but a TV that coversthem all is extremely rare. Most countries now have PAL-BG, including all ofGermany. England has PAL-I, the analog sound is at a different frequency andthe digital sound is their own variety of Nicam. France has Secam L-L', mostlyincompatible with anything else. I don't know about Greece, probably PAL-BG.Most Philips high-end sets can do PAL-BG, Secam-BG and NTSC (the latter fromthe baseband video inputs only). (From: Allan Mounteney (allan@amounten.demon.co.uk)). The answer is YES. Well, at least one. Reason I know is that I was with a company that made computerswith TV-OUT for world wide use and wanted something that couldshow that the TV Out worked for various countries. This ONE and ONLY one we could find Three years ago came fromGermany and covered PAL, SECAM and the American NTSC systems andcame with a note that said from the time of making/selling thatset it would not work in just one small country in South America.All features (including audio) were adjustable from the frontpanel Menu and it was a Grundig 17" job. I am advised that thereis a load of others on the market now. The company who seemed to know all about these international sets and gave us good service at that time was Andrew McCulloch Ltd inCambridge UK. Phone #44(0)1223-351825 Could a TV be modified for 3D (stereo) display?:----------------------------------------------- The whole idea of stereo 3-D vision to put the left and right views to theappropriate eyeball. There are two common ways of doing this: 1. Use different colors for the two views with color filters in from of each eye to separate the views. This is what were often used for the really bad (content wise) sci-fi movies of the '50s. 2. Display alternate views on the same monitor screen but use LCD shutter glasses to allow each eye to only see the appropriate view. This requires increasing the refresh rate to avoid unacceptable flicker. The first approach can be used with any TV and a pair of monochromevideo cameras. Of course, true color cannot be used since pure coloredimages are needed to separate the stereo views. Alternating views with synchronized LCD glasses is a possibility buton a standard TV, the resulting refresh rate would be 30 Hz with a 50%duty cycle which is likely to be useful only as a short experiment - elseyour viewers will likely develop splitting headaches. Displaying TV on a computer monitor:----------------------------------- My general recommendation is that if you have the space, buy an inexpensiveTV - the quality in the end may in fact be better. And, it will be usablewithout tying up your expensive monitor and (maybe) PC. While various convertors are advertized to use a computer monitorwith video from a VCR or other source, keep in mind that if it soundstoo good to be true, it probably is like the claim of a $200 box for this: OK, let me get this straight - this card/box will enable a 31.4 KHz horizontalscan rate monitor (VGA) be used as a TV - yes or no? It thus includes a videoA/D, full screen frame buffer, D/A, and all the other tuner stuff for under$200? I don't think so. A scan doubler - which is a subset of the above -will not result in a high quality picture since it will display pairs oflines interleaved. Or does the impressive advertisement leave out thekey requirement that the monitor sync at the NTSC horizontal scan rateof 15.734 KHz (most newer monitor do not)? Or is it a board that plugsinto a PC and indeed does use the resources of the PC including the VGAcard and bus? In any case, get a written money back satisfaction guarantee. Displaying computer video on a TV:--------------------------------- Assuming this means NTSC: 1. You need to convert RGB to NTSC - there are single chips for this. Try Sony, Philips, Motorola, and others. These will combine the R, G, B, H sync, and V sync into a single composite video signal using a minimum of additional components. 2. You need to match the scan rate to NTSC - 15.734 KHz horizontal. Even basic VGA is twice this - 31.4 KHz. If your video card can be programmed to put out interlaced NTSC rate video then this is easy. If not, it is more difficult. If you want to use anything higher res than VGA, it is a very non-trivial problem requiring the construction of a scan convertor which includes a video A/D, full frame store, interpolator/readout timing, video D/A. Unless you are an experienced digital/analog designer, you really do not want to tackle any of this. For the special case of VGA->NTSC, you may be able to get away with juststoring a single scan line since the horizontal frequency is (almost)exactly twice the NTSC horizontal of 15.734 KHz. A double buffer whereone buffer is storing while the other is reading out at approximately halfthe VGA pixel rate should work. With appropriate timing, even lines become theeven field for NTSC and odd lines become the odd field (I may have thisbackwards). It is still not a trivial undertaking. Also, keep in mindthat the quality you will get on NTSC will be poorer than the VGA due tofundamental NTSC bandwidth limitations. Also, flicker for line graphics willbe significant due to the interlacing at 30 Hz. Even this is a non-trivialundertaking. The requirements for PAL are very similar. For 625 lines systems, the800x600 is the format that most closely matches the TV resolution. You can also buy little boxes to do this. Quality is general not greatas you are seriously limited by NTSC/PAL and the VCR. Except forpresentations on existing TV rate equipment, it is probably not worththe effort. This is totally useless for any serious computer applications. For professional presentations, modern video projectors are available thatuse high resolution LCD panels and real-time scan conversion. However,they are quite expensive (up to $10,000!!!). How can I couple 4 TV screens to make them act like only one?:------------------------------------------------------------- "I've being thinking about how people do these kind of things? Is this analog stuff or do they use some kind of digitized signal which is then divided to each TV?" It is mostly digital. The original master signal is digitized andstored in memory. Control codes specify the readout of a (probably doublebuffered) frame store. 9 and 16 screen versions are common. If youlook closely, you will note that the resolution of pictures that differis always lower indicating that the whole affair is driven from a singletape source with appropriate decoding. Where the pictures are the same,they may be at full resolution. Sub blocks of identical pictures may beat some intermediate resolution. What is Scan Velocity Modulation?:--------------------------------- (From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). Scan velocity modulation occurs around the transients in the luminancesignal. The beam is sped up just before and just after the edge and it isslowed down during the edge. This makes for a sharper edge. On an alternatingB/W pattern (stripes, checkerboard) you will see that the white parts getsmaller and the black parts get whiter. This geometry error is a side-effect.Some say that this is the main intended effect of SVM. SVM is *supposed* to be used to compensate for the spot blowup at high beamcurrent. Peaking does not help to improve sharpness because the higher peakbeam current also gives a fatter spot. SVM *can* work in thatcase. Unfortunately it is often misapplied, too much SVM will give a veryunnatural picture, with obvious horizontal geometry errors. If applied properly, SVM can improve the picture. Unfortunately there has beena rat race, led by Japanese, suggesting that more is better. Some people will simply advise turning the contrast down. At low beam currentthe spot size will be acceptably small and SVM is not needed. In most, if notall, cases they will disable the SVM circuit, usually by pulling the supplyconnector to the SVM panel. That panel is often fixed to the neck of thepicture tube, behind the video amplifier panel. What is Kell factor with respect to interlaced displays?:-------------------------------------------------------- (The following is from Bob Myers (myers@fc.hp.com)). The Kell factor - which has to do with the fact that we're often undersamplingan image from the standpoint of the Gospel According to St. Nyquist - ISa factor in the reduction of vertical resolution, but interlacing playsa part as well. This comes from at least two factors: 1. The receiver usually cannot precisely interleave the two fields. 2. More importantly, there are steps taken to reduce the interline flicker which reduce the effective vertical resolution. This includes running the line width of the display somewhat larger than would otherwise be the case, and in interlaced cameras, discharging the entire screen (including the lines from the "other" field) after every field scanned. Interlace is particularly troublesome on moving images, where you will oftenperceive momentarily "missing" details. There was a LOT of discussionregarding the gory details of interlacing in the recent HDTV debates withinSMPTE and other groups. Homemade V-chip (or at least viewing limiter):--------------------------------------------- Here is an interesting questions: > I would like a control box of some sort that controls the > cable signal that comes into the TV. I want to be able to > control the total time a particular child has in his account to > watch, plus the actual channels that he is allowed to watch > (no Playboy or MTV), PLUS the time of day that he can watch > (not during home work time). Programmable by channel, > cumulative time, hour of the day, and day of the week. I also > need a master pass word for parental programming of the kids > accounts, plus be able to watch what I want to at any time. > The kids could use either an individual account number or an > individual "card" of some kind with a PIN like our ATM cards. > This "box" should be secure so that a 14 year old boy can't > bypass it very easily. At least without doing come major damage > so that I'd know it when he did it. I know that this is a lot > to ask, but I'm very familiar with computer programming and > chipset technology, I do know that such a thing can be done. I > just don't have the electronics knowledge to do it. The following probably won't help you build such a gizmo but hereare some thoughts: First, I would not attempt to build any of the RF/cable switchingstuff - there are too many variations. I would suggest trying tocontrol the control of what you have. With a cable box, this would be relatively easy - just put the box and an IR transmitter in the samesealed enclosure. If you have only a cable ready TV, you could substituteor intercept the remote detector signal inside the set and disablethe front panel controls. Then you need: * An input devices - keypad for example. * A display - a 1 line LCD. * A microprocessor. This doesn't need to be much - just to store the 'account information' including balance, allowable channel and time slot map, passwords. It would need a real time clock. * An IR remote code transmitter. This could probably be directly programmed by the micro to control your cable box. Each account would have a means of adding to the balance,password authentication, etc. You would have a superuser account for your own watching as well aschanging any of the individual account settings. Too bad I don't still teach my intro to computer design courses - thiswould make a nice term project. If you have a junker PC, this would be a simple bit of programming(but quite wasteful of power even for an 8088 based PC). What is Aquadag?:---------------- You may see the term 'Aquadag' referring the the black paint covering theoutside of most of the funnel section of the CRT. (From: Nicholas Bodley (nbodley@tiac.net)). Aquadag used to be a trademark of Acheson Colloids [Corp.?], I thinkaround Niagara Falls or Buffalo, NY. It was one of many "-dag" colloidalgraphites; they also made Oildag, Gredag (grease), and Alcoholdag, as Irecall. Unfortunately, it's probably sold in 55-gallon drums minimum. Ihope you can find smaller quantities. Are there any CRT rebuild shopsaround the USA? See the Thomas Catalog (ThomCat) in a library to findAcheson. I am pretty sure there's nothing magic about the graphite. If you can findsome reasonably-priced nickel-flake or copper-flake paint (be sure it'sconductive!), you might have an affordable (?) coating. How about plainmetal foil, maybe even ordinary aluminum foil? You surely don't needcurrent-carrying capacity; you would need a decent adhesive, though. Howto make sure you have continuity between pieces, I'm not so sure; shootfor really tight crimps that deform the metal and are gas-tight. (Thismight, however, be quite unnecessary.) Combined computer monitor and TV:-------------------------------- "This is a 27" VGA monitor which should also be able to be used as an NTSC television monitor. Can anybody comment on it?" IMO, I think the entire idea of a combined TV/computer monitor is sillyespecially when the likely cost premium is taken into account. Watchingthe boob tube will tie up your entire PC. The optimal size for TV andcomputer use is not the same nor are the requirements in terms of scanrate, resolution, brightness, and sharpness. Thus, the design will beinherently more expensive and include more compromises. So, I will probably be proved wrong by record sales of these things... Interesting TV Switch Mode Power Supply:--------------------------------------- The following was found in a Sony TV: Q1 switching/reg transistor (+) --- ----+------------- ---------------+----------- ---- --- __ AC --- -- = C1 diode /_\ D2 in --- --------- +-----+------+ ---- (-) Reg. Drive C D1 +-----+------+ C choke +---- gnd C __ +135 cap ___ C2 I---> + +----------+----------------+-----------+---- + 135 Although at first this appears to short out the line supply, whendrawn like this it turns out to be a valid switching regulator: Q1 is driven by a pulse width modulated signal a the horizontal rate. Q1 turns on putting 150 V across choke. Current ramps up in choke - more or less linear until saturation which should not occur. This time increases with increasing load. Q1 turns off. Since current in an inductor cannot change instantly, current continues to flow, now through D2, C2, and +135 load. LCR (R of load, diode) time constant - charges capacitor and powers load. It would appear to fail and run away under the following circumstances: 1. Inductance is too low and choke cannot store enough energy even at high duty cycle to supply load. Too high a duty cycle and core saturates at which point transistor blows up. 2. Inductance is too high relative to switching frequency so that choke does not have time to discharge (its current) before next current pulse - DC current will just keep increasing until core saturates. This could only really happen if the switching frequency were too high for some reason unless someone changed core material or something like t. 3. Load is too great due to fault elsewhere. When attempting to diagnose problems with these types of circuits where thenatural outcome of a fault is for one or more expensive parts to failcatastrophically, it is wise to either use a Variac to bring up the inputvoltage slowly and carefully observe the behavior hopefully before too lateor put a load in series with the line such as a 100W light bulb to limitthe current (though this will change the behavior in various ways). The horizontal output transistor substitution jig trick:------------------------------------------------------- (From: penguin@datastar.net). Okay, here's a good trick you can use for almost all tv work. Mount a TO-3transistor socket on a heatsink that has about as much surface area as theskin of both fists balled up, actually the bigger the heatsink the better.Then mount a horizontal output transistor in the socket. Use an ECG238 orequivalent. Make sure you use a good mica insulator, as there will be over athousand volts on the collector. Solder a 1.5 foot red wire (18 gauge or bigger) to the collector, an equal butyellow wire to the base and an equal but green wire to the emitter (or useyour own color codes). You may be able to salvage a ready made heatsink withsocket out of an old receiver or TV. Mine came out of some old Curtis MathesTV's. Solder a damper diode with the cathode to the collector and the anodeto the emitter. Add a 200 ohm 1/4 watt resistor from base to emitter. Addthese parts to the socket not the transistor, so the transistor can easily bechanged if you ever need to. Now you have a very useful test jig. If you are ever working on a TV that hasa blown HOT (horizontal output transistor) you can pull out the bad part andconnect this jig. Then you can run the set at low voltage. If you have a set where the HOT is running too hot, this method often willgive you some running time, hopefully enough time to find out what the problemis. Often the bad parts themselves will self destruct or heat up to whereidentifying them is easy. Usually a bad flyback will crack and smoke provingitself to be bad. Once your satisfied that the problem is cured, you can putthe original HOT in knowing it will be safe. Usually when I power a TV in this way (using a Variac) I'll bypass the seriespass regulator with a jumper. This is easily done by finding the 180 to 330ohm 15 to 20 watt regulator bypass resistor and putting a jumper across it.With the regulator bypassed the power supply will go to 160 volts this is whyit is necessary to use a Variac and only run it at about 60 volts. It isnecessary when using this brute force approach, to make sure that all of thelow voltage supplies coming off the flyback are fused with fusibleresistors. Most models do fuse the LV supplies, but some don't. (Oneparticular RCA comes to mind.) ?Another good trick, if your out in thefield and don't have a varactor handy, is to simply pull the series passregulator (e.g. STR30130 etc.) and let all the power just come through the 20w bypass resistor. If the flyback is okay the B+ to the flyback will come upto about 60 to 90 volts, and in many cases you can even see a dim picture.?Anything less than 50-60 volts and the flyback is probably bad. Don't run itthis way for more than a minute or two as the the resistor will be dissipatingclose to or more than its rated power under these circumstances. Of coarse youobviously can't use this method with switching power supplies. Here's a good trick for the Sony tv's that use the SG-613, even though thisdevice is a gate controlled SCR you can sub a regular HOT like the ECG238 onyour test jig. I used to blow out these buggers to the tune of about $20dollars a pop til I figured out how to use the "HOT Heatsink Jig". Now withthe jig connected, the horizontal width may not open up all the way, but youcan run these old Sony's like this for about 5 minutes before the HOT jigstarts to get too hot. Usually if they run this long they're ok and then youcan put the SG-613 in knowing that you aren't going to see a bunch of $$$ goup in smoke. I had a Sony that would run for weeks then blow the SG-613finally put this one to rest when I changed out the horizontal outputtransformer which was separate from the flyback on this oldie. Always be cautious of the high voltage on the collector of the HOT JIG. Ken's comments on (TV) SMPS repair:---------------------------------- (From Kenneth Aaron (kennetha@geocities.com)). 1. NEVER NEVER NEVER power on a SMPS without load, the newer ones especially in TVs (not so much VCRs) self destruct when not loaded. 2. The light bulb test is great to see if your SMPS can handle the load of the horizontal circuits - when the set does not turn on - you get the initial power on then it goes off - best is to disconnect the collector of the horizontal output transistor and plug in a light bulb and see if it goes on. 3. Chinese TVs have poor quality capacitors - the latest models mostly have the same SMPS so this applies for all. There is a small electrolyte cap in the supply feedback about 22 to 47uF at 50V. This dries up real fast and after 2 years or so the voltage B+ goes up from 110 V to anything up to 300 V! (not joking here). I got a tv where the end of the tube was blown off from a supply that reached 296 V instead of 105 V. that's over 75KV into the screen! 4. The newer Philips and copycat Chinese models use the main supply to power the horizontal. The flyback is driven by a transistor which has over 2500 V on it's collector. The flyback is built differently as well. These transistors are called 2DS... - do not use a replacement - I did use one with a higher voltage and it fried - this is because the ceramic capacitors around it along with it's different characteristics changed the 'on' time and it overheated after a few minutes. 5. You can always use a BU208D instead of a BU208A, BU508D instead of BU508A, etc, the extra diode will do no harm. IR detector circuit:------------------- This IR Detector may be used for testing of IR remote controls, CD playerlaserdiodes, and other low level near IR emitters. Component values are not critical. Purchase photodiode sensitive to nearIR - 750-900 um or salvage from optocoupler or photosensor. Dead computermice, not the furry kind, usually contain IR sensitive photodiodes. Forconvenience, use a 9V battery for power. Even a weak one will work fine.Construct so that LED does not illuminate the photodiode! The detected signal may be monitored at the collector of the transistor (Q1)with an oscilloscope. Vcc (+9 V) >-------+---------+ \ / / R3 \ R1 \ 500 / 3.3K / \ ____ _\_/_ LED1 Visible LED ____ IR ----> _/_\_ PD1 +--------> Scope monitor point Sensor Photodiode B / C +------- Q1 2N3904 \ E \ / R2 +--------> GND \ 27K / GND >--------+---------+ __ - UK Satellite TV information:--------------------------- (From: Martin Pickering). Here is a list of the FAQs and other documents related to UK satellite TVavailable at: * http://www.netcentral.co.uk/satcure/ by adding the appropriate file name to the URL, above, or following the links. aegir.htm The Aegir/Dixi/Lenco/Oritron Jupiter D2Mac decoder FAQchurchil.htm The Alfaglade Churchill D2Mac decoder FAQd2mac.htm A general discussion about buying D2Mac decodersdigifaq.htm Chris Moore explains Digital Satellite Receiversdiseqc.htm An explanation of DiSeqCdummies.htm Satellite TV for the beginnerfilmnet.htm Philips BBD-901 FilmNet D2Mac decoder FAQgalaxis.htm Galaxis digital receiver specificationsgrd150.htm Grundig GRD150/200/280/300 receiver FAQinterf.htm A discussion about picture interference problemsjack.htm Lots of humorous stories originally published in magazineslnb.htm A discussion about various LNBs and frequenciesmoney.htm How to make money from Satellite TV!mrd920.htm Pace MRD920 D2Mac receiver FAQmss200.htm Pace MSS200/Apollo receiver FAQmss500.htm Pace MSS500/1000 receiver FAQnimbus.htm Mimtec Nimbus receiver FAQprdkits.htm Upgrade kits for Pace PRD receivers explainedproducts.htm Index page for SatCure productsreliable.htm A discussion about making your receiver more reliablesat1700.htm Nokia SAT1700 receiver FAQsataccs.htm SatCure accessories pagesatbooks.htm SatCure books pagesatfaqs.htm Index page for all FAQssatkits.htm Satcure repair/upgrade kits pagesatwalk.htm A discussion about the SatWalker and other motorised unitsscarts.htm A discussion about Scart connectors - which is best?spares.htm A complete price list of SatCure component sparessparkly.htm A discussion about "sparlies" ("fischen") and the curessr5500.htm Echostar SR5500 receiver FAQsrd400.htm Amstrad SRD400 receiver FAQsrd500.htm Amstrad SRD500 receiver FAQsrd510.htm Amstrad SRD510 receiver FAQsrd600.htm Amstrad SRD600 receiver FAQsrx200.htm Amstrad SRX200 receiver FAQss9kits.htm Upgrade kits for Pace SS9xxx receivers explainedsvs250.htm BT-SVS250 receiver FAQtools.htm A discussion about repair toolsuniden.htm Uniden UST- receiver models FAQwhich.htm Which receiver shall I buy?advice.htm What to do if your receiver will not work?ard200.htm Cambridge ARD200, BT-SVS200, JVC TU-AD1000 receiver FAQctu900.htm Philips CTU900 D2Mac decoder FAQmss100.htm Pace Prima/MSS100 receiver FAQprd.htm Pace PRD800/900 receiver FAQrd480.htm Cambridge/Matsui RD480 Extra receiver FAQsrd6.htm Ferguson SRD6 receiver FAQsrd700.htm Amstrad/Fidelity SRD700, SR950, SR950+ receiver FAQss9.htm Pace SS9xxx receiver FAQsvs300.htm BT-SVS300 receiver FAQwhy.htm "Why am I in business" - a discussion for when you're down!yourfaqs.htm Copies of questions and answers - let's have more! *************** International Color Television Standards *************** Brief description of international color TV standards:----------------------------------------------------- (The following is from Bob Myers: (myers@fc.hp.com)). Well, the joke was that SECAM stands for System Essentially Contrary tothe American Method....:-) The basic, oversimplified description of the three common encoding methodsis as follows: NTSC: Used in North America, Japan, and a few other areas. Luminance ("blackand white" information) is sent just as it was before color, and colorinformation is provided in two "color difference" signals (actually, derivedalong with the luminance (Y) signal) via matrix multiplication) whichare carried on a "color subcarrier". The chroma (color) signals are severelyband-limited compared to the luminance signal, which is one reason you cannever fully recover proper RGB from an NTSC-encoded signal. The color information itself is encoded such that the PHASE of the chroma signals,relative to the reference signal, is important in recovering the color.As used in the U.S., the broadcast standard provides a line rate of approx.15,734.26 Hz, and a field rate of 59.94+ Hz* PAL: Very similar to NTSC, with the exception that the phase of the colorsubcarrier is reversed on alternate lines; this tends to cancel some ofthe more common color errors seen in the NTSC system. (The color signalsof PAL are also simple color-difference signals, rather than using the moreinvolved RGB -> YIQ matrix of NTSC). In the most common European PAL broadcast systems, a line rate of 15,625 Hz and a field rate of 50.00 Hsare used*. SECAM: This system is very different from both NTSC and PAL. Luminance andcolor-difference signals are still used, but the color difference signalsare sent separately, on successive lines. This requires at least a one-linememory or delay line be provided in the receiver for proper color decoding.The broadcast SECAM systems usually use similar line/field rates as forthe PAL broadcast standards noted above*. * - Note: In all three cases, the terms "NTSC", "PAL", and "SECAM" technically refer only to the COLOR-ENCODING systems described above; they do not specifically imply a set of timing standards or frequencies. The one possible exception to this is the use of the term "NTSC", since the U.S. National Television Standards Committee ALSO came up with various timing standards for U.S. television. But in all cases, the color encoding method is not *strongly* tied to a specific line/field timing. For example, there is at least one broadcast system (Brazil's) which uses NTSC encoding, but at the line/field rates more commonly seen in the European systems. Some questions and answers about TV standards:--------------------------------------------- (Responses from: Steve McKinty: (smckinty@france.sun.com)) > 1. What are the most common TV standards in the world? NTSC: National Television Standards CommitteePAL: Phase Alternate LineSECAM: SEquential Couleur Avec Memoire (Sequential colour with memory) There are other differences though. Strictly they are just differentcolour systems, but most countries which use PAL have 625 lines ina picture and send 25 full pictures/second, most NTSC countries have525 lines and send 30 full pictures/second (mostly for historicalrather than technical reasons). That complicates things. > 2. Who devised them, and when? and why? Are they as old as television? The first serious TV experimenting was done in several countries aroundthe period 1900-1930, mostly black & white. The BBC started a regularservice in 1936, other countries followed soon after, but since thetechnology was developing very rapidly there were always improvementsbeing made. The BBC started with 405 lines, the US started a servicea couple of years later with 525, by the time other European countriesstarted the technology allowed 625 lines. France even tried 819 lines. All those system were black & white, but people wanted to havecolour. During the 1940's much of Europe was at war, and technologicaldevelopment for entertainment slowed down, but in the US theywere able to continue and devised a colour system which wascompatible with the existing black & white one. By compatible I mean that a black & white TV got a black & whitepicture, a colo(u)r one got a colour picture. No need to make peoplethrow away their B&W TVs. This system was endorsed by the AmericanNational Television Standards Committee, and was named after it => NTSC. After the war other countries started to look at colour. NTSC was avery clever system, but it had some flaws. Engineers in variouscountries tried to improve on it, and Telefunken in Germany came upwith a simple modification which improved colour stability. Itwas named PAL because they reversed the Phase of the colour signal onAlternate Lines. At the same time Henri de France, in France, fixed the same flaw ina different way. His design (SECAM) needed a memory inside the setwhich made it more expensive. PAL gave as good a result, so mostcountries opted for that. France stayed with SECAM, possibly becausein the De Gaulle era of the 50's memories of German occupation werestill fresh, and dropping a French system in favour of a German onewould have been unpopular. Rumour has it that the French governmentsubsidized Thompson to make memory affordable. Since Britain went PAL, France went SECAM, and the US went NTSC, anycolonies or dependencies of those countries tended to get the samesystem. India/Pakistan got PAL, Algeria got SECAM, and since theUS helped rebuild Japan after WW2 it got NTSC, etc. > 3. What's the difference? To squeeze a colour signal into the same space as a black & white one,and stay compatible, the NTSC designers separated the colour andbrightness information. The human eye is less sensitive to colour, sothey were able to reduce the bandwidth of that signal (make it takeup less space in each channel), 'hiding' it at the high-frequencyend of the video. That meant they didn't need to make the channelsbigger, and incompatible. To do that, they used the fact that you can represent most colourswith a combination of Red, Green and Blue. If you film a scenewith three cameras, one for each colour, then add all theoutputs together you get a black & white image. This signalis called luminance, usually represented by 'Y'. MathematicallyY = R + G + B. (Actually, not all the contributions are equal). They then transmitted the Y signal just as for a black & white TV,and also transmitted the R and B in the extra colour signal. B&W TV'sonly saw Y, and colour TV's got Y, R and B. Since Y = R + B + G, G canbe obtained as Y - (R+B), so they didn't need to transmit all three. To get both R and B into one signal, they use a combination ofPhase and Amplitude modulation (think of it as AM and FM at the sametime). Its called quadrature modulation, and works very well, but issusceptible to phase changes as it passes along cables, etc. If thesignal gets +10 degrees phase change the colour will visibly change,which is why NTSC TV's have a tint control. PAL overcomes that by sending R and +B on one line, then R and -B onthe next. That way a +10 phase shift on one line becomes -10 on the next,and small differences will cancel out. PAL TV's don't need tint controls.(Some old PAL sets may have a one, however). SECAM doesn't send both R & B together, it sends R on one line, B onthe next. No fancy modulation, so no phase problems, but you need a'memory' in the set to save up the signal from the previous line,since both R & B are required together for processing. > 4. Why do you need different TVs? Mostly because of the different numbers of lines. Its quite easy tomake one colour decoder which can cope with all the systems, butmaking a TV which can do 625 and 525 lines, 25 and 30 pictures/second,gets expensive. Consumers shop on price, no-one will buy a SECAMTV in the USA even if it only costs $20 more, since there aren'tany SECAM channels. > 5. Why do you need different VCRs? Why can't one VCR record the> same "output"? Some can, but like TVs it costs more to make them adjust. The motorspeed varies with the number of pictures transmitted per second, forexample. (This is covered in more detail in the document: "Notes onthe Diagnosis and Repair of Video Cassette Recorders".) > 6. Why did different systems evolve? Is one cheaper? Is one better? When originally developed, expense was considered based on contemporarytechnology. As noted, politics may have been equally important. As to which has better quality, its all rather subjective. The625-line system adopted in Europe has better vertical resolutionthan the 525-line US system, but some people find the 50Hz field ratestill produces some flicker. NTSC/PAL/SECAM are all equally capableof excellent colour reproduction, but under poor signal conditionsNTSC can degrade more quickly. > 7. Are there other systems besides the ones I've mentioned? Why? Some others, like MAC where the colour and luminance are completelyseparated. That gets rid of interference (ever see the strangecolours which appear on very fine check patterns?) but is moreexpensive and really only possible due to modern electronics. > 8. Are there going to be more or less systems in the future? That is THE question! There are certainly going to be differentsystems, more lines, better sound, etc. > 9. Is there any way to convert a PAL tape to NTSC or vice versa? Yes. If the PAL tape has 625 line pictures and the NTSC one has 525 linethen you normally need a computer which can read in one format andre-adjust things. Not cheap, but becoming cheaper, several companiesoffer that sort of service. Some PAL VCRs can do a half-conversion,enough to fool most PAL TVs into thinking its got a PAL signal. > 10. Do they teach this stuff in electrical engineering courses? Sometimes. Some of it, depends a lot on the course and school. Politically Correct TV Standards:-------------------------------- (The following is from: Robert Rolf). SECAM: Used by France and the former Soviet union. No tint control. No color control. Full socialism. The state knows exactly what color you should see, and how strong that color should be. PAL: Used by Germany & UK, Australia etc. No tint control. A color control. Partial socialism. The state knows exactly what color you should see, but you get a choice as to how strong it can be. NTSC: Used in USA and Canada, Japan etc. A tint control, A color control. Uncontrolled socialism. The state lets you chose what color you see and how strong it can be. They then tax you regardless. Just another way of looking at it.... Variations on a 'standard' - the PAL system:------------------------------------------- In the U.S., when PAL is mentioned, it is usually assumed to be 625 line/50 Hzas used in the UK and man other places. However, there are several variationson the PAL system. (The following from: Ed Ellers Somewhere on the chassis there may be an inked chassis number; an examplefor one color set was TS-914. A chassis number will at least get you someservice information, and should be all you need unless you plan to try toget cabinet parts for it (chortle guffaw titter). Number should be findableon the back of the chassis (i.e. where the pots are mounted through thechassis). Techical assistance help numbers:-------------------------------- Here are contact numbers for some TV manufacturers: Curtis Mathis 1-800-949-4999 Steve Long Mitsubishi 1-800-552-8324 NAP 1-900-896-8324 Zenith 1-800-874-1930 ext 1065 or 1066 1-800-856-0981 1-312-745-5154 Sanyo 1-800-877-5032 Panasonic 1-201-348-7957 1-201-348-7958 1-201-392-6961 1-201-392-6992 Web resources:------------- Many manufacturers are now providing extensive information via theWorld Wide Web. The answer to you question may be a mouse clickaway. Perform a net search or just try to guess the manufacturer'shome page address. The most obvious is often correct. It will usuallybe of the form "http://www.xxx.com" where xxx is the manufacturers' name,abbreviation, or acronym. For example, Hewlett Packard is hp, SunMicrosystems is sun, Motorola is, you guessed it, motorola. Electronicparts manufacturers often have detailed datasheets for their productofferings. Tandy (Radio Shack) has a nice web resource and fax-back service. This ismostly for their equipment but some of it applies to other brands and thereare diagrams which may be useful for other manufacturers' VCRs, TVs,CD players, camcorders, remote controls, and other devices. http://support.tandy.com/ (Tandy homepage) http://support.tandy.com/video.html (Video products) http://support.tandy.com/support_video/2846.htm (TVs) In addition to Tandy products, there is at least one Sony model. Furthermore,since Tandy does not manufacture its own TV sets - they are other brands withRealistic, Optimus, or other Radio Shack logos - your model may actually becovered. It may just take a little searching to find it. The one below is specifically for the Sony KV-F29 but I assume it applies toother Sony models as well. It provides a source of technical serviceinformation and includes Sony KV-F29 related Service Bulletins: * http://www.healey.com.au/~nu-lifetv/tech/kvf/ Parts information:----------------- I have found one of the most useful single sources for generalinformation on semiconductors to be the ECG Semiconductors MasterReplacement Guide, about $6 from your local Philips distributor.STK, NTE, and others have similar manuals. The ECG manual willenable you to look up U.S., foreign, and manufacturer 'house' numbersand identify device type, pinout, and other information. Note thatI am not necessarily recommending using ECG (or other generic) replacementsif the original replacements are (1) readily available and (2) reasonablypriced. However, the cross reference can save countless hours searchingthrough databooks or contacting the manufacturers. Even if you havea wall of databooks, this source is invaluable. A couple of caveats:(1) ECG crosses have been known to be incorrect - the specificationsof the ECG replacement part were inferior to the original. (2) Don'tassume that the specifications provided for the ECG part are identicalto the original - they may be better in some ways. Thus, using the ECGto determine the specifications of the parts in your junk bin can be risky. Other cross reference guides are available from the parts source listed inthe section: "Repair parts sources". Suggested references:-------------------- Some good sources for technology information: * Basic Theory of Colour Television Philips Ask for this book from your local technical bookstore. * Basic Television & Video Systems, 5th ed. Bernard Grob McGraw Hill For a technical reference on the various flavours of NTSC, PAL, and SECAMused around the world, I suggest: * Recommendations and reports of the CCIR volume XI, Part 1 Available from Omnicom, 115 Park St. S.E. Vienna, VA 22180 (703)281-1135 It following book is for PAL TV-standard specifications: * Colour Television (With particular refererence to PAL) G.N. Patchett. Norman Price (Publishers) Ltd. It has three heavyweight chapters describing NTSC/PAL/SECAM and has a decentamount of math content. The following is more directed toward digital video but may still containsome information useful for understanding analog TV technology: * Video demystified: A handbook for the digital engineer Keith Jack Brooktree Corporation, 1993 ISBN 1-878707-09-4 There don't seem to be nearly as many TV repair books for modern solidstate TVs as I recall for old tube sets. Here are a couple which you mayfind (or its predecessor) at your local public library (621.384 if youlibrary is numbered that way) or a technical book store. MCM Electronicshas the Davidson as well. * Troubleshooting and Repairing Solid State TVs Homer L. Davidson 2nd Edition, 1992 (The 1st edition is also useful) TAB Books, Inc. Blue Ridge Summit, PA 17214 * Basic Television Principles & Servicing Bernard Grob The following is a recent publication: * Troubleshooting and Repair Guide to TV PROMPT Publications (Howard W. Sams), (800) 428-7267. ISBN #0-7906-1077-9, $29.95. From the advertising blurb for this book: "This book, 300 pages of detailed photos, schematic diagrams, and text explains in easy to understand language how TV works, how to troubleshoot problems, and advice on how to fix them. The Howard W. Sams Troubleshooting and Repair Guide to TV is the perfect reference book for technicians, instructional guide for students and hobbyists." FCC ID Numbers of TVs:--------------------- Only a few manufacturers actually produce the vast majority of TVs. Forexample, Radio Shack, Magnavox, and Emerson do not make their own TVs (Ican tell you are not really surprised!). How do you determine the actual manufacturer? For most types of consumerelectronics equipment, there is something called an 'FCC ID' or 'FCC number'.Any type of equipment that may produce RF interference or be affected bythis is required to be registered with the FCC. This number can be usedto identify the actual manufacturer of the equipment. A cross reference and other links can be found at: http://www.repairfaq.org/REPAIR/F_FCC_ID.html Interchangeability of components:-------------------------------- The question often arises: If I cannot obtain an exact replacement orif I have a monitor, TV, or other equipment carcass gathering dust, can Isubstitute a part that is not a precise match? Sometimes, this is simplydesired to confirm a diagnosis and avoid the risk of ordering an expensivereplacement and/or having to wait until it arrives. For safety related items, the answer is generally NO - an exact replacementpart is needed to maintain the specifications within acceptable limits withrespect to line isolation, X-ray protection and to minimize fire hazards.Typical parts of this type include flameproof resistors, some types ofcapacitors, and specific parts dealing with CRT high voltage regulation.However, during testing, it is usually acceptable to substitute electricallyequivalent parts on a temporary basis. For example, an ordinary 1 ohmresistor can be substituted for an open 1 ohm flameproof resistor to determineif there are other problems in the horizontal deflection circuits beforeplacing an order - as long as you don't get lazy and neglect to install theproper type before buttoning up the monitor or TV. For other components, whether a not quite identical substitute will workreliably or at all depends on many factors. Some deflection circuits areso carefully matched to a specific horizontal output transistor that nosubstitute will be reliable. Here are some guidelines: 1. Fuses - exact same current rating and at least equal voltage rating. I have often soldered a normal 3AG size fuse onto a smaller blown 20 mm long fuse as a substitute. 2. Resistors, capacitors, inductors, diodes, switches, potentiometers, LEDs, and other common parts - except for those specifically marked as safety-critical - substitution as long as the replacement part fits and specifications should be fine. It is best to use the same type - metal film resistor, for example. But for testing, even this is not a hard and fast rule and a carbon resistor should work just fine. 3. Rectifiers - many are of these are high efficiency and/or fast recovery types. Replacements should have at equal or better PRV, Imax, and Tr specifications. 4. Posistors - many of these are similar. Unfortunately, the markings on the devices are generally pretty useless in determining their ratings. Note, however, that the prices for replacement posistors may be quite reasonable from the original manufacturer so it may not make sense to take the risk of using an unknown part. (From: Stefan Huebner (Stefan.Huebner@rookie.antar.com)). In most cases you can use a standard 3-terminal-device, the resistance of the temperature dependent resistors in it are nearly identical. Here is a list of possible replacement devices: 380000-01, 24340521, 2199-603-1201, 163-024A, 163-035A, CO2200-N66, C8ROH, QX265P05503, 32112026, 4822-A1-11240148, 02199-003-120, 15-08-001A, 5391560067, F400001. 5. Transistors and thyristors (except HOTs and SMPS choppers) - substitutes will generally work as long as their specifications meet or exceed those of the original. For testing, it is usually OK to use types that do not quite meet all of these as long as the breakdown voltage and maximum current specifications are not exceeded. However, performance may not be quite as good. For power types, make sure to use a heatsink. Also see the section: "Replacement power transistors while testing". 6. Horizontal output (or SMPS) transistors - exact replacement is generally best but except for very high performance monitors, generic HOTs that have specifications that are at least as good will work in many cases. Make sure the replacement transistor has an internal damper diode if the original had one. For testing with a series light bulb, even a transistor that doesn't quite meet specifications should work well enough (and not blow up) to enable you to determine what else may be faulty. The most critical parameters are Vceo/Vcbo, Ic, and Hfe which should all be at least equal to the original transistor. I have often used by favorite BU208D as a temporary substitute for other HOTs and SMPS (chopper) transistors. Make sure you use a heatsink and thermal grease in any case - even if you have to hang the assembly by a cable tie to make it fit. For that matter, you can usually substitute a similar HOT with the D suffix instead of the A (or no) suffix. These have a built-in damper diode and two in parallel (the external one) will not hurt (or remove it). Naturally, the reverse is not true since a damper diode IS essential and the HOT will probably not last beyond the click of the power relay without one! For an explanation of what the damper diode does, see: * http://www.repairfaq.org/REPAIR/sam_test/F_deflfaq.html On SVGA monitors, there will likely be additional circuitry between the HOT and the damper so this trick doesn't work for them. However, using an HOT with much better specs may actually result in early failure due to excessive heating from insufficient and/or suboptimal base drive. See the document: "TV and Monitor Deflections Systems" for more info. 7. Deflection yokes - in the old days, particularly for B/W TVs, all of these were quite similar. It was common to just swap with one that fit physically and at most need to adjust or change a width coil. With color TVs and high performance multiscan monitors, this is no longer the case. Sometimes it will work but other times the power supply won't even be able to come up as a result of the impedance mismatch due to different coils and pole piece configurations. In addition, there may be other geometry correction coils associated with the yoke that could differ substantially. However, if you are really determined, see the section: "Swapping of deflection yokes". Also see the section: "Replacement power transistors while testing". 8. Standby power transformer - this most likely only has a single secondary so locating a standard UL approved (for safety reasons) power transformer with the same output voltage should not be difficult. Check the service manual or the Sams' Photofact for the set to determine the required output voltage and if a centertap is needed. Current should be quite low. 9. CRTs - aside from the issues of physical size and mounting, many factors need to be considered. These include deflection angle, neck diameter, base pinout, focus and screen voltage requirements, purity and convergence magnets, etc. Color CRT replacement is rarely worth the effort in any case but trying to substitute a different CRT is asking for frustration. For monochrome CRTs, there is less variation and this may be worth a try. 10. The following are usually custom parts and substitution of something from your junk box is unlikely to be successful even for testing: flyback (LOPT) and SMPS transformers, interstage coils or transformers, microcontrollers, and other custom programmed chips. Horizontal output transistor pinouts:------------------------------------ You will nearly always find one of two types of horizontal output transistorsin TVs and monitors: * Metal can - TO3 package: _ / O \ View from bottom (pin side) / o o \ ( B E ) B = Base, E = Emitter, C = Collector \ / \ O / C The metal case is the Collector. * Plastic tab - TO3Pn (n = several suffixes) package: _____ / \ O View from front (label side) B = Base, E = Emitter, C = Collector _______ If there is an exposed metal tab, this is the Collector as well. B C E Some other transistor types use the same pinout (TO66 for metal can, TO218and TO220 for plastic tab) but not all. However, for horizontal outputtransistors, these pinouts shouuld be valid. Note that those with a built in damper diode may read around 50 ohms betweenB and E (near 0 on the diode test range) - this is normal as long as theresistance is not really low like under 10 ohms. How do you locate the HOT:------------------------- Well, it is usually the LARGEST transistor in the set near the LARGESTtransformer in the set (flyback - the thing with the FAT red wire connectingto the picture tube) on the LARGEST heat sink in the set. Got that? :-) Or, in the good old days.... (From: Don Wall (d.wall@nunet.neu.edu)). Sure, it's usually the largest tube in the set, has a top cap, runs very hot,and is often a 6BQ6G or some such. (tongue firmly in cheek) Actually, back inthe days of yore, the Horizontal Output Tube was frequently referred to as theHOT; guess some things don't change! Replacement power transistors while testing:------------------------------------------- During testing of horizontal deflection circuits or switchmode power supplies,particularly where the original failure resulted in the death of the HOT orchopper, overstress on replacement transistors is always a possibility if alldefective components have not be identified. Therefore, using a part with better specifications may save you in the longrun by reducing the number of expensive blown parts. Once all other problemshave been located and repaired, the proper part can be installed. However, this is not always going to work. In a TV and especially a highperformance monitor, the HOT may be closely matched to the drive and outputcomponents of the deflection circuits. Putting in one with higher Vce, I,or P specifications may result in overheating and failure due to lower Hfe. Where possible, a series load like a light bulb can be used limit the maximumcurrent to the device and will allow you to power the equipment while checkingfor other faults. Some designs, unfortunately, will not start up under theseconditions. In such cases, substituting a 'better' device may be the bestchoice for testing. (From: Glenn Allen (glenn@manawatu.gen.nz)). I been repairing SMPS of all types but when I started on those using MOSFETsI was blowning a few of them when replaced because something else was faulty. Ever since I have been using a BUZ355 on a heat sink I haven't blown it. Itis rated at 800 V, 6 A, and 220 W. it is a TO218 case bigger than a T0220.It seems the higher ratings allows you to do repair where as a something like a 2SK1117 or MTP6N60 will just blow. Testing of replacement HOTs:--------------------------- The following is useful both to confirm that a substitute replacement HOT issuitable and that no other circuit problems are still present. However,single scan line anomalies (particularly when changing channels and/or wherereception is poor with a TV or when switching scan rates and/or when no orincorrect sync is present with a monitor) resulting in excessive voltageacross the HOT and instant failure are still possible and will not resultin an HOT running excessively hot. (From: Raymond Carlsen (rrcc@u.washington.edu)). After installing a replacement HOT in a TV set or monitor, I like to check thetemperature for awhile to make sure the substitute is a good match and thatthere are no other problems such as a weak H drive signal. The input currentis just not a good enough indicator. I have been using a WCF (well calibratedfinger) for years. For me, the rule of thumb, quite literally, is: if you cannot hold your finger on it, it's running too hot, and will probably failprematurely. Touching the case of the transistor or heat sink is tricky.... Metal case transistors will be connected to the collector and have a healthypulse (>1,200 V peak!) and even with plastic case tab transistors, the tab willbe at this potential. It is best to do this only after the power is off andthe B+ has discharged. In addition, the HOT may be hot enough to burn you. A better method is the use of an indoor/outdoor thermometer. I bought onerecently from Radio Shack for about $15 (63-1009). It has a plastic 'probe' onthe end of a 10' cable as the outdoor sensor. With a large alligator clip, Ijust clamp the sensor to the heat sink near the transistor and set up thedigital display near the TV set to monitor the temperature. The last TV I usedit on was a 27" Sanyo that had a shorted H. output and an open B+ resistor.Replacement parts brought the set back to life and the flyback pulse lookedOK, but the transistor was getting hot within 5 minutes... up to 130 degreesbefore I shut it down and started looking for the cause. I found a 1 uF 160volt cap in the driver circuit that was open. After replacing the cap, Ifired up the set again and monitored the heat sink as before. This time, thetemperature slowly rose to about 115 degrees and stayed there. I ran the setall day and noticed little variation in the measurement. Test equipment doesn'thave to cost a fortune. Removing and replacing the deflection yoke:------------------------------------------ Should you need to remove the deflection yoke on a color CRT, some basicconsiderations are advised both to minimize the needed purity and convergenceadjustments after replacement as well as to prevent an unfortunate accident. The position and orientation of the yoke (including pitch and yaw) and magnetassembly (purity and static convergence rings, if used) are critical. Usepaint or White-Out(tm) to put a stripe across all of the magnet rings so youwill know their exact positions should they accidentally shift later. If thereare rubber wedges between the yoke and the funnel of the tube, assure that theyare secure. Tape them to be doubly sure as adhesive on old tape dries up withage and heat and becomes useless. This will avoid the need for unecessarydynamic convergence adjustments after reassembly. The neck is the most fragile part of the CRT so do not apply any seriousside-ways force and take care not to bend any of the pins when removing andreplacing the CRT socket. The yoke and purity/static convergence assemblies will be clamped and possiblyglued as well. However, the adhesive will probably be easily accessible - bigglobs of stuff like hot melt glue and/or RTV silicone. Carefully free theadhesive from the glass neck of the CRT. Loosen the clamps and gently wigglethe magnets and yoke off the neck. They may appear stuck from age and heatbut should yield with gently persuasion. Once the yoke is replaced, some fine adjustments of the picture rotation,purity, and static and dynamic convergence may be needed but hopefully withyour most excellent diagrams, these will be minimal. Similar comments apply for monochrome CRTs but there are far fewer issues asthe yoke is positioned firmly against the funnel of the CRT and rotation andcentering are usually the only adjustments. However, there may be magnetslocated on swivels or glued to strategic locations on the CRT envelope tocorrect for geometric distortion. Swapping of deflection yokes:---------------------------- This should work with identical TVs or monitors. Your mileage will vary ifyou are attempting a swap between monitors with similar specifications.Chances of success for monitors with widely different screen sizes or scanrate specifications is close to zero. One indication of compatibility problems would be major differences inresistance readings for the corresponding yoke windings, CRT HV and otherbias levels, etc. Before you do the transplant, see the section: "Removing and replacing thedeflection yoke" for procedures and precautions to minimize problems inrealignment. Make a precise diagram of everything you do. Keep the purity/static convergence magnet assembly with the original CRT ifpossible and install it in the same or as nearly the same position as possiblewhen you replace it. Once you are sure of the connections, power it up carefully - there is noassurance that your yokes are compatible. A yoke with a much lower resistanceor inductance than the original may overstress components in the power supply. You will then need to go through all the adjustments starting with purityand convergence. Swapping of CRTs:---------------- Given the problems of just replacing a CRT with an identical new one, it isn'tsurprising that attempting to substitute a CRT which is not the same type willresult in difficulties - to say the least. Obviously, the closer in size,scan rate (for monitors), and deflection angle, the more likely the chancesof success. Where the alternative is to junk the TV or monitor, it may beworth a shot - and you may get lucky! It may be best to transfer as much as possible with the CRT - yoke and purityand convergence magnets. The connectors to the yoke may need to be changedbut this may be the least of your problems. Difference in yoke impedance andother characteristics may result in anything from incorrect size to a trulyspectacular melt-down! The latter is much more likely with SVGA monitorscompared to similar size/deflection angle TVs. Where the neck size is the same, the yoke can be moved from one CRT to theother but you will have to do a complete purity and convergence set up andeven then you may have uncorrectable convergence errors. See the section:"Swapping of deflection yokes". (From: J. G. Simpson (ccjgs@cse.bris.ac.uk)). Monitors are generally designed by choosing a CRT, then the EHT, then designinga yoke to scan the CRT, then designing a driver circuit to drive the yoke. In a CRT test lab it's common to have variable supplies for EHT and othervoltages, a small selection of yokes, and variable amplitude drive circuits. EHT affects scan sensitivity, brightness, spot size. You can't get highbrightness and small spot size on a large monitor with 3 KV of EHT. Virtuallyevery variable has some effect on convergence. Spot size is important, in asmuch as you want most of it on the phosphor and not the shadow mask. Provided the neck size is the same you can swap tubes in yokes but don't expectit to work very well. Different tube manufacturers may use radically differentgun structures. A given yoke and its driver may give underscan or overscan andit's pretty well certain that convergence will be way off. The military spends a small fortune on trying to get the drop into the yoke andit flies with no adjustment or convergence CRT. For the rest of us swapping aCRT is a pain in the butt. Decayed glue in electronic equipment:------------------------------------ Larger components like electrolytic capacitors are often secured to thecircuit board with some sort of adhesive. Originally, it is white andinert. However, with heat and age, some types decay to a brown, conductiveand/or corrosive material which can cause all sorts of problems includingthe creation of high leakage paths or dead shorts and eating away at nearbywiring traces. The bottom line: Most of the time, this stuff serves no essential purposeanyhow and should be removed. A non-corrosive RTV or hot-melt glue can beused in its place if structural support is needed. Repair parts sources:-------------------- For general electronic components like resistors and capacitors, mostelectronics distributors will have a sufficient variety at reasonablecost. Even Radio Shack can be considered in a pinch. However, for consumer electronics equipment repairs, places like Digikey,Allied, and Newark do not have the a variety of Japanese semiconductorslike ICs and transistors or any components like flyback transformers ordegauss Posistors. The following are good sources for consumer electronics replacement parts,especially for VCRs, TVs, and other audio and video equipment: * MCM Electronics (VCR parts, Japanese semiconductors, U.S. Voice: 1-800-543-4330. tools, test equipment, audio, consumer U.S. Fax: 1-513-434-6959. electronics including microwave oven parts and electric range elements, etc.) Web: http://www.mcmelectronics.com/ * Dalbani (Excellent Japanese semiconductor source, U.S. Voice: 1-800-325-2264. VCR parts, other consumer electronics, U.S. Fax: 1-305-594-6588. car stereo, CATV). Int. Voice: 1-305-716-0947. Int. Fax: 1-305-716-9719. Web: http://www.dalbani.com/ * Premium Parts (Very complete VCR parts, some tools, U.S. Voice: 1-800-558-9572. adapter cables, other replacement parts.) U.S. Fax: 1-800-887-2727. * Computer Component Source (Mostly computer monitor replacement parts, U.S. Voice: 1-800-356-1227. also, some electronic components including U.S. Fax: 1-800-926-2062. semiconductors.) Int. Voice: 1-516-496-8780. Int. Fax: 1-516-496-8784. For those hard-to-find or overpriced TV replacement boards, modules, or otherparts, try: * PTS Electronics Corporation. - Bloomington, Indiana (National Headquarters): 1-800-844-7871 - Arvada, Colorado: 1-800-331-3219 - Tustin, California: 1-800-380-2521 Email: pts@ptscorp.com Web: http://www.ptscorp.com/. Also see the documents: "Troubleshooting of Consumer Electronic Equipment" and"Electronics Mail Order List" for additional parts sources. -- end V2.65 --

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